Add new temporary ext.CodeMirror.visualEditor.init RL module which
selects the temporary ext.CodeMirror.visualEditor.v6 or non-v6 based on
$wgCodeMirrorV6. This will allow us to deploy CM6 further.
As a result of this work, the core CodeMirror class now has knowledge
of ve.ui.Surface.
Other changes:
* Add Compartment for specialCharsExtension so it can be disabled in VE.
* Add option to mediaWikiLang() to disable template folding.
* Add support for RTL wikis where $wgCodeMirrorRTL is enabled.
* Make CodeMirror.logUsage() and setCodeMirrorPreference() static.
* Fix unit and linting tests.
Some code courtesy of Fandom, GPLv2-or-later; see:
https://github.com/Wikia/mediawiki-extensions-CodeMirror/commit/ef297c48c
Bug: T357482
Change-Id: I15453b33e77e1c1b4d5e5183e41e53d56ff14c3e
