Create a page for every enum in RNA_enum_items.h, which includes
the enum values and the doc-string for each item.
Each page creates a references which the API reference can be linked to
via the same name as the enum, so :ref:`rna_enum_icon_items` links
to the list of icons for e.g.
This has two main advantages:
- No need to manually duplicate enum values in the doc-strings of
functions defined in Python's C/API (not RNA defined functions),
`bpy.props` for example.
- The generated Python API docs can reference these instead of including
the enums in-line - resulting in unreasonably long lists in the case
if icons and event types (for example).
These changes will be made separately.
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