Rename widgets two pane sheet layout files and spec files to more fitting name

Currently the names used for widgets two pane sheet files are similar to full sheet files, just with "_large_screen" added to it. This is not a good name as it can cause confusion. The new name includes "_two_pane" which is more indicative of the actual functionality of these files.

Fix: 276917926
Test: verify widget picker two pane still works
Change-Id: I23cf2a20fc137cc3e99c5fdc90100648a0926368