Fix crash in BrightnessDialog

I couldn't reproduce this brash with the TOT build, but
based on the stack trace attached in the bug, I think
this cl would fix it.

Root cause:
The original code added an OnAttachStateChangeListener to the
window's DecorView to initialize Compose. This caused an
`IllegalStateException` because the DecorView already had a
LifecycleOwner from the Activity. And this Activity is the
`android.app.Activity`, which is extened by the BrightnessDialog,
it did not correctly provide the LifecycleOwner and
SavedStateRegistryOwner required by Jetpack Compose.

In this change:
  - The problematic OnAttachStateChangeListener is removed.
  - Instead of Activity, let BrightnessDialog to extend
`androidx.activity.ComponentActivity`, which provides the
necessary LifecycleOwner and SavedStateRegistryOwner
implementations out of the box.
  - The corresponding unit test was updated to invoke onResume
on the main UI thread via runOnUiThread. This is necessary
because lifecycle methods must be called on the main thread,
a requirement enforced by ComponentActivity.

Bug: 417544544
Flag: com.android.systemui.qs_ui_refactor_compose_fragment
Test: Manually.
Change-Id: Ia3bf5b0a9b84f46db0665049b852d8d6aeebf39e