Fix create page markdown toolbar visibility

[hjiangsu]

Pull Request Description

This PR potentially fixes an issue where the markdown toolbar is not visible when the keyboard is opened. I haven't been able to reproduce this issue myself, so this fix is a general guess and would have to be tested on an affected device.

The potential fix is to apply a margin equal to the keyboard's height for the toolbar, such that when the keyboard is open, the markdown toolbar is shifted up by the same amount. I've also set resizeToAvoidBottomInset to be false so that the scaffold does not automatically scale the page (which might potentially cause overflow issues that may hide the toolbar as well?)

@micahmo if you could just do a quick test on this on your device and let me know if the toolbar still shows up properly on your end, that would be great!

Issue Being Fixed

Issue Number: #1575

Screenshots / Recordings

Checklist

• If a new package was added, did you ensure it uses an appropriate license and is actively maintained?
• Did you use localized strings (and added appropriate descriptions) where applicable?
• Did you add semanticLabels where applicable for accessibility?

[micahmo]

Tested locally and it seems to work well!