Keypress should not happen during composing (as spec) but it does on Windows for Korean IMEs

Closes #5316

Fix for mouse events that get sent to the wrong document when the script is being run in a different frame than the editor. 

Closes #5221

Closes #5217

Issue #5061

Issue #5054

See https://github.com/codemirror/CodeMirror/commit/79d266e60a8d02a865c7cf9340628a0f5d920394#commitcomment-25055107

That overlay modes can use to access the underlying token info.

Since it produces orderings that don't correspond to what
the browser does then.

To take document direction into account

Closes #4878.

Issue #4926

Closes #4975. Checking `hasFocus` is a reasonable idea, but in Firefox
`hasFocus` returns false on `mousedown` if the window, but not the document
was focussed before. This leads to a wrong cursor in `contenteditable`
input style.