Adds a UiAutomation#clearCache() to be consistent with A11yService.

Includes a @TestApi for CTS testing that the cache was cleared, also
copied from A11yService.

Bug: 263394275
Test: atest AccessibilityCacheTest
Change-Id: Ia5fee5d13c6e4949ae1206edd9f0b22e53f0a437
3 files changed