Indent editor in TalkSectionAddOverlay

Wrap editor in panel and move padding for wikitexteditor from Overlay
to EditorOverlay (it is specific to it).

Bug: T74969
Change-Id: Ie721c6e39d0cf8d1082f2420c6d68d1e88b08c3b
Merge "Indent editor in TalkSectionAddOverlay"