Add two new actions for the 'preview' feature:
* preview-realtime-on – The WikiEditor 'Preview' toolbar button
was clicked to turn the preview panel on.
* preview-realtime-off – The WikiEditor 'Preview' toolbar button
was clicked to turn the preview panel off.
* preview-realtime-inuse – Fired without user interaction when the
WikiEditor preview feature is already on when the editing form is
opened.
This also adds a new hook for the last of these to use and to match
the enable/disable hooks.
Bug: T298218
Change-Id: I1a2545c2b0491c1d07f9508fab70967d03d61594
Store the current state (enabled/disabled) of Realtime Preview in
a new user preference `wikieditor-realtimepreview` and set it
when enabling or disabling the preview pane.
Bug: T294599
Change-Id: Id5f51c6d77ed0077906d5d5178cbfa785cc04dcf
* Toolbar button to toggle a two-pane layout on and off.
* Resizable bar for the width of the two panes.
* Resizable bar for the edit box height, even when realtime preview is off.
* Only enabled when $wgWikiEditorRealtimePreview = true.
* Fires JS hooks when enabled, resized, and disabled.
Bug: T293347
Change-Id: Id09d44519249c0b7f5c33d48d524b7c92a5a9106
