feat(developer): support FollowKeyboardVersion in kmc-package

Fixes #7340.

Removes the unused <Version> element from <LexicalModel> element in the
.kps schema. (This needs to be copied to api.keyman.com also.)

Updates compiler to check for <FollowKeyboardVersion> and read the
version data from the .kmx in that case.

Unit tests updated. Some of the fixtures were incorrect as they had
<FollowKeyboardVersion> set for model-type packages or packages that
contained no keyboards. Fixed.