Re-used existing route and moved tinymce help to its own different
route. Added test to cover.
Added new external-content block to support in editor UI.
Prevents polluting global scope with variables since we're using the
module format bundler in esbuild.
Also cleaned up unused yields.
Fixed bad reference in our tinymce fixes.
For #5232
Added new options that sits on the context, for things needed but not
for the core editor, which are defined out of the editor (drawio URL,
error message text, pageId etc...)
Started basic playground for testing lexical as a new WYSIWYG editor.
Moved out tinymce to be under wysiwyg-tinymce instead so lexical is the
default, but TinyMce code remains.
