"Show Texture in texture tab" button: full support for Sculpt / Paint

In {rBb279fef85d1a} the button that displays a texture in a Properties
Editor texture tab was added for geometry nodes.
Same commit will actually show them for Brush textures as well (but
disabled -- because the Texture users dont match).
This task is for finanlizing proper support for Brush textures as well.
There was originally a separate patch for this (see {D9813}) but most of
it was already implemented by above commit.

**what this solves**
from the default startup file:
- go to any sculpt or paint mode and add a texture to your brush
- observe the button to edit this texture in the Properties editor is
greyed out

{F9860470}

There are two possible solutions:
- [1] call the texture template for the brush `texture_slot` texture
(instead of the brush 'texture') from the python UI code, this is then
working in harmony how ButsTextureUser works for brushes
- [2] tweak the way `ButsTextureUser` works (dont rely on
`RNA_BrushTextureSlot` there)

This patch implements the first solution.
Since `brush.texture_slot` is `br->mtex` RNA wrapped and `brush.texture`
is `br->mtex.tex` RNA wrapped, this really comes down to doing the same
thing. I checked that creating a new texture and unlinking/deleting will
have the same results even though they take slightly different code
paths: assignment and NULLing the pointers are working on the same (see
above) and RNA update callbacks also do the same [even though in
different functions]:
- brush.texture will do rna_Brush_main_tex_update
- brush.texture_slot.texture will do rna_TextureSlotTexture_update /
rna_TextureSlot_update
(only difference here is an additional DEG relations update in the case
of texture_slot which should not do harm)

Differential Revision: https://developer.blender.org/D10626

release/scripts/startup/bl_ui/properties_paint_common.py

@@ -277,11 +277,10 @@ class TextureMaskPanel(BrushPanel):
         layout.use_property_decorate = False
 
         brush = context.tool_settings.image_paint.brush
+        mask_tex_slot = brush.mask_texture_slot
 
         col = layout.column()
-        col.template_ID_preview(brush, "mask_texture", new="texture.new", rows=3, cols=8)
-
-        mask_tex_slot = brush.mask_texture_slot
+        col.template_ID_preview(mask_tex_slot, "texture", new="texture.new", rows=3, cols=8)
 
         # map_mode
         layout.row().prop(mask_tex_slot, "mask_map_mode", text="Mask Mapping")

release/scripts/startup/bl_ui/space_image.py

@@ -1189,9 +1189,10 @@ class IMAGE_PT_tools_brush_texture(BrushButtonsPanel, Panel):
 
         tool_settings = context.tool_settings.image_paint
         brush = tool_settings.brush
+        tex_slot = brush.texture_slot
 
         col = layout.column()
-        col.template_ID_preview(brush, "texture", new="texture.new", rows=3, cols=8)
+        col.template_ID_preview(tex_slot, "texture", new="texture.new", rows=3, cols=8)
 
         brush_texture_settings(col, brush, 0)
 

release/scripts/startup/bl_ui/space_view3d_toolbar.py

@@ -631,10 +631,10 @@ class VIEW3D_PT_tools_brush_texture(Panel, View3DPaintPanel):
 
         settings = self.paint_settings(context)
         brush = settings.brush
+        tex_slot = brush.texture_slot
 
         col = layout.column()
-
-        col.template_ID_preview(brush, "texture", new="texture.new", rows=3, cols=8)
+        col.template_ID_preview(tex_slot, "texture", new="texture.new", rows=3, cols=8)
 
         brush_texture_settings(col, brush, context.sculpt_object)
 
@@ -658,8 +658,9 @@ class VIEW3D_PT_tools_mask_texture(Panel, View3DPaintPanel, TextureMaskPanel):
         brush = context.tool_settings.image_paint.brush
 
         col = layout.column()
+        mask_tex_slot = brush.mask_texture_slot
 
-        col.template_ID_preview(brush, "mask_texture", new="texture.new", rows=3, cols=8)
+        col.template_ID_preview(mask_tex_slot, "texture", new="texture.new", rows=3, cols=8)
 
         brush_mask_texture_settings(col, brush)