[ticket/12093] Check that document.selection is supported.

PHPBB3-12093
Merge remote-tracking branch 'remotes/prototech/ticket/12093' into develop-olympus

* remotes/prototech/ticket/12093:
  [ticket/12093] Check that document.selection is supported.
Merge branch 'develop-olympus' into develop

* develop-olympus:
  [ticket/12093] Check that document.selection is supported.

Conflicts:
	phpBB/adm/style/editor.js
	phpBB/assets/javascript/editor.js
	phpBB/styles/prosilver/template/editor.js