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
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.