If there is no TOC in the current document, it's created at current
cursor position. Subsequent generation calls update TOC at existing
position.
Add additional tests with CodeMirror editor mock.
Adds table of contents for any Markdown note or
Markdown snippet.
Consequent generations update existing TOC.
Generated TOC is case sensitive to handle #2067
Shortcut : CommandOrControl+Alt+T
Menu : Edit/Generate/Update Markdown TOC
