[gtk] (12 commits) ...Merge branch 'matthiasc/builder-requires' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  db6d7dc... Drop “gtk+” plus sign in GtkBuilder <requires>. (*)
  e6d46ec... Teach `gtk-builder-tool` to rewrite <requires>. (*)
  08f2990... Document the GtkBuilder <requires> tag changes. (*)
  f7de0bc... Fix tests with regard to GtkBuilder <requires>. (*)
  d69a943... gtk: Remove <requires> from ui files (*)
  d6c753b... gtk4-demo: Remove <requires> from ui files (*)
  9b056f5... examples: Remove requires from ui files (*)
  18779b9... testsuite: Remove <requires> from ui files (*)
  e4be785... builder: Be a bit more strict about requires (*)
  7215c74... buildertool: Supplant a requires (*)
  d6a0948... testsuite: Update buildertool tests (*)
  74a7f73... Merge branch 'matthiasc/builder-requires' into 'master'

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