[gtk] (21 commits) ...Merge branch 'wip/matthiasc/shared-glyph-cache' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  66b081d... glglyphcache: Use stb_rect_pack for better glyph packing (*)
  b74bb90... gl renderer: Move texture atlas into its own file (*)
  e2ffad7... glimage: Only support uploading one region (*)
  cf4ff56... gl renderer: Add & use icon cache (*)
  adb5df0... glyph cache: Clarify message (*)
  a375793... gl: Free icon data (*)
  f37274d... gl: Don't leak texture atlases (*)
  2529385... glyph cache: Reinstate 1 pixel padding (*)
  102cc1c... gl: Add 1 pixel of padding in the icon cache (*)
  efc3116... gl: Allow setting min/mag filter on textures (*)
  4020399... gl: Use linear scaling for atlases (*)
  c9cea36... gl: Use pad-extend for icon cache (*)
  7293fd5... glyph cache: Stop storing driver and render (*)
  1f70bc4... gdk: Create a global shared GL context (*)
  259bbdc... Share glyph and icon caches (*)
  ecb353f... Consider all offscreen drawings for the icon cache (*)
  054b521... Remove debug spew (*)
  e961943... Fix a refcounting mishap (*)
  d90143d... texture atlas: Add a missing initialization (*)
  0dcb717... Cosmetics (*)
  c168116... Merge branch 'wip/matthiasc/shared-glyph-cache' into 'maste

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