fix(developer): version string matches for sentry

Fixes two things:
* $VERSION_GIT_TAG was being misinterpreted by mkver as
  $VERSION + "_GIT_TAG". This has been addressed by making the $VERSION
  match the last one in the replaceVersionStrings_Mkver function, and
  also have moved to using the newer $VersionGitTag and $Environment
  vartiables instead.
* The 'dist' property was being set in sentry-cli sourcemap uploads,
  though we never set the dist prop when we initialize sentry.