cdp: add input.insertText

[krichprollsch]

Relates with #1148

[karlseguin]

can do it separately, but I sometimes see el.blur() being called, which could impact how/where this behaves. (I think in DDG)

[krichprollsch]

I agree, we have work to do regarding that:

• dispatch events on text selection, focus and blur
• listen these events to maintain a document's (or window) state of active element and selected text (I know active_element is in the document's state)
• implement Selection API

I will write an issue for all of that.