FindwxWidgets: Add support for wxWidgets 3.0.0 (#14587)

Add the "wxWidgets-3.0.0" path suffix and the "30" library names.
While at it, add the "wxWidgets-2.9.5" suffix too.
Order cmGeneratorTargets deterministically.

Use a string as the key in a map, instead of a cmTarget*.
Merge topic 'use-generator-target' into next

940229c Order cmGeneratorTargets deterministically.
Merge topic 'FindwxWidgets-3.0.0' into next

2cd5597 FindwxWidgets: Add support for wxWidgets 3.0.0 (#14587)