Add a stock Format menu to MiniBrowser

Add a stock Format menu to MiniBrowser
https://bugs.webkit.org/show_bug.cgi?id=166804

Reviewed by Andy Estes.

* MiniBrowser/mac/MainMenu.xib:
Many of the features automatically work with editable web views.
However, this seems to expose a bug where none of the font-related features
(Cmd-B, for example) work until the first time the font panel is shown,
per process, which will need to be investigated separately.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@210485 268f45cc-cd09-0410-ab3c-d52691b4dbfc