Only refresh TaskThumbnailViewDeprecated if runningTaskShowScreenshot has changed

- This is a follow-up of ag/28922223, which caused a RECENTS_SCROLLING jank regression
- The regression is probably caused by TaskThumbnailViewDeprecated unnecessarily redrawing, the fix is to only redraw when needed
- Also combined setShouldShowScreenshot and refreshThumbnails into a single method, so we can easily check inside TaskView if a refresh is necessary
- Centralize screenshotTasks logic into RecentsViewUtils, and centralize thumbnailView refreshing inside TaksView.setShouldShowScreenshot

Fix: 362294538
Test: Invoke Omnient or Screenshot hardware button on live tile, verify running task switches to screenshot after overlay closes
Test: Select/Screenshot swithces to screenshot normally
Flag: EXEMPT BUG_FIX
Change-Id: I7c6e73e52ebf18e7c59bb9afea029246b92681d2