Move widget files into widget folder + add tests.

I will use the newly created LauncherAppWidgetProviderInfoTest in a follow-up CL to add tests for the newly added widget sizing APIs.

Test: Automatic: Ran all robolectric tests in launcher3,
      Manual: Added a widget, edited the widget, removed the widget
Bug: 179807199
Change-Id: I540b2dbe284c6eb5aa2466a1d13a9581ee59425b
44 files changed