Media picker: Action sheet for other media sources appears out of place on iPad

[rachelmcr]

Expected behavior

When I add media from another source (free photo library, Giphy, other apps) I expect the action sheet to choose the source to appear near the toolbar/bottom of the screen in the editor.

Actual behavior

When I tap the ellipsis to choose another media source:

The action sheet to choose the media source appears in the top left:

Steps to reproduce the behavior

1. Open the editor on an iPad.
2. Tap in the post content area.
3. Tap the + toolbar button to add media.
4. Tap the ellipsis to add media from another source.

Tested on [iPad Mini], iOS [12.0.1], WPiOS [11.6.0.20190116]

[ngoctr]

I noticed this happened when working on #13803. The reason is that the underlying anchor view for the popover has been disappeared when the keyboard being resigned. @frosty I made a quick fix to show the sheet in the center screen as follow. Please let me know if you are happy with this, so I will put it in the PR for #13803. Thanks James.

[frosty]

Thanks @ngoctr! However, would it be possible to open a separate PR for that fix, as it's kind of distinct from the Tenor changes?

[ngoctr]

Sure @frosty, it should be. I will submit a separate PR for this one.

[ScoutHarris]

Fixed with #13841.