Make redraw faster when scrolling picker values

[ArnOmsft]

Content refreshing is not catching up when scrolling UIPicker. Repro steps:

• Open WOC Catalog Release or Debug -Tap Pickers -Quickly swipe the pickers to scroll values (this is most noticeable with the minute and year values)

RESULT: Redraw is very slow

[andrejo-msft]

From #1488 -

Phone: Lumia 640 device (14393 build) Master commit: 3a18ee2 Build/run WoCCatalog in Release. Bring up PageView. Click on arrows. Expected: transition of PageView is fluid Actual: transition of PageView from one page to another flickers significantly on the first three loads, then becomes less pronounced (but visible) in subsequent transitions.

Mentioned by @bebauer-msft: Found an additional issue that may result from this flickering. If you tap pages fast enough and happen to tap during transition (in the flickery part), you will end up losing one of the pages and making the paging completely broken.