[geary] (15 commits) ...Merge branch 'mjog/composer-context-loading-fixes' into 'mainline'

[Michael Gratton <mjog src gnome org>]

Summary of changes:

  2030b2d... test: Break out engine mock objects into their own name-spa (*)
  35683dd... build: Reduce verbosity of meson vars by removing `geary_`  (*)
  6e0aa31... build: Generate client internal VAPI and build client tests (*)
  8608293... Application.AccountInterface: New interface for accessing a (*)
  2957f15... Geary.RFC822.MailboxAddresses: Update equality semantics (*)
  c41515a... Geary.RFC822.MessageIDList: Replace append with concatenate (*)
  c73888b... Geary.RFC822.MessageIDList: Support merging message id list (*)
  ea5c95b... Trivial code formatting fixup (*)
  691a239... Composer.ApplicationInterface: New composer app interface (*)
  a781e0e... Composer.WebView: Rework HTML consts so that IDs have inter (*)
  1ed1f82... Composer.Widget: Rename `get_composed_email` to `to_compose (*)
  44654e3... Composer.Widget: Rework context email loading (*)
  29ba931... Composer.Widget: Handle non-Geary HTML and plain text draft (*)
  e5bfd72... test-client: Fix test failure for new composer widget tests (*)
  e5247a2... Merge branch 'mjog/composer-context-loading-fixes' into 'ma

(*) This commit already existed in another branch; no separate mail sent