Refactor BubbleControllerTest for coverage & best practices.

This commit introduces FlagsParameterization to the BubbleControllerTest
to increase test coverage for different flag configurations.
Additionally, this commit adheres to Mockito's best practices for
Kotlin, improving test readability and maintainability.

Bug: 387193964
Flag: EXEMPT refactor
Test: atest WMShellRobolectricTests:BubbleControllerTest
Test: atest WMShellMultivalentTestsOnDevice:BubbleControllerTest
Change-Id: Iea4d720e22933330e351e5dbaefb5e787a6c0b92