This renames the mode identifiers to be consistent with e.g. the context mode identifiers and other names used for the new Grease Pencil.
For `object.mode`:
* `PAINT_GPENCIL` -> `PAINT_GREASE_PENCIL`
* `SCULPT_GPENCIL` -> `SCULPT_GREASE_PENCIL`
* `VERTEX_GPENCIL` -> `VERTEX_GREASE_PENCIL`
* `WEIGHT_GPENCIL` -> `WEIGHT_GREASE_PENCIL`
For the internal `ob->mode` flag:
* `OB_MODE_PAINT_GPENCIL_LEGACY` -> `OB_MODE_PAINT_GREASE_PENCIL`
* `OB_MODE_SCULPT_GPENCIL_LEGACY` -> `OB_MODE_SCULPT_GREASE_PENCIL`
* `OB_MODE_VERTEX_GPENCIL_LEGACY` -> `OB_MODE_VERTEX_GREASE_PENCIL`
* `OB_MODE_WEIGHT_GPENCIL_LEGACY` -> `OB_MODE_WEIGHT_GREASE_PENCIL`
Resolves#127374.
Pull Request: https://projects.blender.org/blender/blender/pulls/128604
5f5b1b83d0