Bundled themes: Add editor styles for form elements

[pbiron]

Please add editor styles for basic form elements, e.g.:

• input[type=text]
• input[type=submit]
• etc

I am developing a block that generates a custom search form for a CPT. On the front-end, the block is styled by whatever the current theme uses for such elements.

It would be great if Twenty Seventeen had editor styles for those elements so that it looked the same in the editor.

I have opened this ​same issue on GitHub for Twenty Nineteen.

Doing this for all Twenty XXX themes would be great, but Twenty Seventeen & Nineteen are the only really important ones for me.

[pbiron]

Now that the ​GitHub Issue for for Twenty Nineteen has been closed, I just want to reiterate here the need for this in Twenty Seventeen and Twenty Nineteen.