Draft: Rename build options in line with Gnome guidelines

Contains two commits to bring the build options into line with Gnome guidelines and make consistent witth gegl see : https://wiki.gnome.org/Initiatives/GnomeGoals/MesonPorting. This may well have downstream consequences but I think that it is probably a worthwhile change.

1:

• removes the enable- / with- prefixes from the build-options (Gnome meson porting guidelines)
• changes the option gir to introspection and vapi to vapigen (align with GEGL)
• changes vapigen & lcms options to type feature (align with GEGL)
• adds two new CI build options to test auto features with/without dependencies present.

2:

• changes introspection option from combo to feature - this does not change the way the build behaves but does allow the gir build to be controlled with the -Dauto_features switch