We should be using the new name for the enum value instead
of the old one in the enum class docstring.
Move the old compatible name to an extra note
"Available as ``xx.yy`` in older QGIS releases."
Fixes#49171
This ensures that we correctly apply filters to recent projections
too, eg so that a widget showing only vertical crs will ONLY show
recent VERTICAL crs, not every recent crs.
Cleanup QgsProjectionSelectionWidget to use proper models to
drive the combo box. This removes a bunch of very fragile
logic regarding showing and hiding entries on demand, as it
allows us to move all the filtering logic to a single place
in a QSortFilterProxyModel subclass.
This has a few side benefits:
- The combos now dynamically respond to changes like recent
CRS being used in other places in QGIS
- The widget correctly respects horizontal/vertical crs filters
for all entries, including recent crs
