Fix #128079: Grease Pencil stroke direction overlay missing on 4.2 LTS

Caused by the wrong uniform function being called.

This was not creating issue on opengl because sizeof(bool) is
4 for uniform boolean. But on metal, the boolean are packed
in 1 byte each which was triggering an assert and Undefined
behavior.

To be landed in 4.2. The 4.3 doesn't have GPv2 overlays.

Pull Request: https://projects.blender.org/blender/blender/pulls/129307

source/blender/draw/engines/overlay/overlay_gpencil_legacy.cc

@@ -347,7 +347,7 @@ static void OVERLAY_edit_gpencil_cache_populate(OVERLAY_Data *vedata, Object *ob
     const bool show_direction = (v3d->gp_flag & V3D_GP_SHOW_STROKE_DIRECTION) != 0;
 
     DRWShadingGroup *grp = DRW_shgroup_create_sub(pd->edit_gpencil_points_grp);
-    DRW_shgroup_uniform_float_copy(grp, "doStrokeEndpoints", show_direction);
+    DRW_shgroup_uniform_bool_copy(grp, "doStrokeEndpoints", show_direction);
 
     blender::gpu::Batch *geom = DRW_cache_gpencil_edit_points_get(ob, pd->cfra);
     DRW_shgroup_call_no_cull(grp, geom, ob);