A variety of operators were missing appropriate bl_options for correct
undo support.

This results in either crashes (auto loft, bi-rail) or other odd
behaviors around returning the scene to the correct previous state
(sometimes having to hit ctrl-z twice to undo once, sometimes undo skips
steps, etc.)

Differential Revision: https://developer.blender.org/D13283

Add guards to the functions triggered by checkbox updates
in the preferences.  This prevents them from being called
multiple times, such as when the mouse is hovered over
the checkbox and the backspace key is repeatedly pressed.

glTF exporter: performance: cache parent/children data to avoid bad .children performance when used a lot
Thanks rotoglup!

Ref D15432

Currently, the nodes in the Switch menu (Shift+S) are generated from Node
Wrangler's own long static list of categories and nodes, which often goes
out of sync when Blender changes.

This changes to using the node_categories_iter utility which uses the correct
list of available nodes from nodeitems_builtins.py.

The submenu classes are now procedurally generated and registered in the same
fashion as the add menu, but just with a different operator in their draw
function.

Removing the static lists required a couple changes outside of the Switch menu.
Mostly having to compare types using the verbose node.rna_type.identifier.

Includes improvements on the original patch by Benni Merz.

No need to subtract scroll bar widths as they are hidden by default in 2.80+.

The Operator is internally called "Swap Links" and the manual also calls it
"Swap Links" as it can swap inputs and outputs.

Differential Revision: https://developer.blender.org/D10031

Add utility function to check for the first output that is actually enabled
rather than always using the first output of a node.

The previous behavior would lead to confusing situations, where a mix/math
node was added but didn't seem to be connected, when the first output was
currently disabled.

Differential Revision: https://developer.blender.org/D14251

* The added nodes are now top aligned with the nodes they belong to. This looks
  nicer and works independent of screen DPI.
* There is a vertical offset based on the socket the added nodes are connected
  to. This prevents nodes from overlapping too much, when executing the texture
  setup several times in a row.
* Ignore disabled sockets, which would create nodes seemingly connected to
  nothing.

Differential Revision: https://developer.blender.org/D15031

Both the "Libraries" panel and the "Current Blend's Folder" button are
meant for the File Browser editor, not the Asset Browser.

Fixes T94212

The regular Save operator does not automatically save changes in images,
users become aware of this when quitting Blender or changing files.

This became a problem for the Save/Reload operator since you'd lose work
without noticing it. This commit adds a check and let the user now in the
terminal which image files have not been saved.

Fixes T73905

Related to T98252

The code was looking for background images in the 3D Viewport, which have
been moved to Camera objects in 2.8.

Fixes T98252

Based on suggestion from D13223, but applied a different fix.

Feature removed in rBAb56a6acb9f4f.

Part of T80730

Part of T80730

Part of T80730

Part of T80730

The warning "In heavily development, things may change" is no longer true,
and can be removed.

The pose library has quite nice documentation. It would be a shame if
nobody would find it.

Fix when animation are not baked

Group the three reference fields that have to be cleared to
generate a completely new rig in a box. Also clarify the name
and tooltip for Force Widget Update.

Requested by @dexon, see rBAece39d809ce#339214.

This patch tries to improve a workflow that was hurt by D11356.
One of the goals of that patch was to make the connection between
metarig and generated rig stronger and more reliable, by using
datablock pointers rather than text-based matching. This allows
users to rename their datablocks as they would do with any other
datablock in Blender, so there's much more freedom with naming
when working with one metarig per generated rig per file.

However, this made it hard to duplicate the metarig, make changes
to it, and make a new rig out of it within the same file. Renaming
several datablocks in this case is not an "option", but an unintuitive
necessity.

With the patch applied, when the metarig has no target rig, there is
an option to input a rig name. If something is input by the user, that
name will be used for the rig, the widget collection (by extension the
widget objects) and the rig script, as long as they are not specified.

So, while still requiring a few more clicks than before, the workflow
for duplicating metarigs to make new ones is now much more reasonable:

- Duplicate metarig, make changes
- Remove the datablock references
- Input a rig name
- Generate

If the a rig object with the same name already existed, it will NOT be
overwritten, and the generated rig will have a .001 suffix. This matches
the "new" option of the removed "new/overwrite" options.

Meanwhile, the other workflow of having one metarig per generated rig
per file is not affected at all: The text box for the name input can
simply be ignored on the first generation. It will not show up after
that, since you would never remove the target rig in this workflow.

Differential Revision: https://developer.blender.org/D14757

Only consider local datablocks when searching for the rig object,
widget collection and widget objects themselves during generation.

Edit mode represents bone orientation via their head and tail
locations, plus a roll value. This math has a singularity in
the -Y direction, resulting in instability and discontinuity
for bones exactly aligned to the Y axis (the tail flips the
deform bones, so +Y is also bad).

The only reliable way to avoid problems is to un-align the
bones via very small offsets in the Z direction.

Support for BoundaryRule (how to handle edges/vertices in subdivision
surface) was added in rBA9a285d80167f, but the values between
'CreaseAll' and 'CreaseEdge' were inverted.

Reviewed By: mont29

Differential Revision: D15035

Set parent of eye and nose bones to head instead of left ear.

Differential Revision: https://developer.blender.org/D15347