Re-design of submodules used in blender.git

This commit implements described in the #104573.

The goal is to fix the confusion of the submodule hashes change, which are not
ideal for any of the supported git-module configuration (they are either always
visible causing confusion, or silently staged and committed, also causing
confusion).

This commit replaces submodules with a checkout of addons and addons_contrib,
covered by the .gitignore, and locale and developer tools are moved to the
main repository.

This also changes the paths:
- /release/scripts are moved to the /scripts
- /source/tools are moved to the /tools
- /release/datafiles/locale is moved to /locale

This is done to avoid conflicts when using bisect, and also allow buildbot to
automatically "recover" wgen building older or newer branches/patches.

Running `make update` will initialize the local checkout to the changed
repository configuration.

Another aspect of the change is that the make update will support Github style
of remote organization (origin remote pointing to thy fork, upstream remote
pointing to the upstream blender/blender.git).

Pull Request #104755