Blender Git Loki

Fix #26218: texture paint
- Added option "Fixed Texture" to the UI. Because of strange reason,
this feature was implemented but hidden from users.
Would be cool, if somebody familiar with 2d texture paiting check.
- Fixed some issues in existing code of fixed texture paiting.
It now handles brush radius and curve correct.
- Also fixed issue with paiting with texture from node tree - it used
to be painted with regular brush color instead of texture.