Create WM Shell Flicker helper library

So that Flicker tests in other places can make use of the Splitscreen utils and avoid copying the utils all over the place.

Test: atest WMShellFlickerServiceTests WMShellFlickerTestsSplitScreen
Change-Id: I5db19729c3968aba66dc3dfce1f3eafe9f1a0972
66 files changed