Fix error in DecorView's ViewConfiguration

In ViewConfiguration, we use isUiContext to verify if a context
is an visual context. However, DecorContext uses Application
context as a base context and return false as intended.
This patch overrides isUiContext to report context#isUiContext
instead.

fixes: 153664027
Test: atest DecorContextTest#testIsUiContextFromVisualDecorContext
Change-Id: Ida26b9617c74dc6997fc2c00d97d3420a0978fc7