WYSIWYG: Added text direction support for code editor popup

WYSIWYG: Added text direction support for code editor popup

Editor popup will now reflect the direction of the opened code block.
This also updates in-editor codemirror instances to correcly reflect/use
the direction if set on the inner code elem.

This also defaults new code blocks, when in RTL languages, to be started
in LTR, which can then be changed via in-editor direction controls if
needed. This is on the assumption that most code will be LTR (could not
find much examples of RTL code use).

Fixes #4943