Custom Properties: allow changing the property UI to color picker.

To fully support storing colors as a custom property, it is necessary
to allow switching the property UI to the standard color picker button.
That means in effect supporting custom property subtype values.

Change RNA_property_subtype to look for a 'subtype' string field
in _RNA_UI and parse it as an enum value. To minimize performance
impact, only do it if the property is an array; also, don't use
the custom subtype during RNA path parsing.

On the python side, allow setting some most useful seeming values
from the custom property settings editor.

Also, since some color picker code seems to run into a risk of
buffer overruns if the array size is wrong, check the size in
the UI layout code to be safe.

Reviewers: campbellbarton

Differential Revision: https://developer.blender.org/D5475

release/scripts/modules/rna_prop_ui.py

@@ -159,6 +159,7 @@ def rna_idprop_ui_create(
         soft_min=None, soft_max=None,
         description=None,
         overridable=False,
+        subtype=None,
 ):
     """Create and initialize a custom property with limits, defaults and other settings."""
 
@@ -195,6 +196,9 @@ def rna_idprop_ui_create(
         if default and (not is_array or any(default)):
             rna_ui["default"] = default
 
+        if is_array and subtype and subtype != 'NONE':
+            rna_ui["subtype"] = subtype
+
     # Assign other settings
     if description is not None:
         rna_ui["description"] = description