Lower macOS deployment target to 10.10 on Intel

After switching to use the builtin libwebp, we can do this and support
back to 10.10 (or the oldest version the specific Python version
supports), which is the oldest version supported by wxWidgets.

Closes: #2901

Drop upload of demo/docs to extras - replaced by release

Upload snapshot builds to GitHub pre-releases (instead of wxpython.org)

This is mainly to migrate snapshot builds off wxpython.org and onto
something more reliable.

Release 4.2.5

Release 4.2.4

Release 4.2.3

Update version to 4.2.2