Clean up computeValue()

This method has become a god method, many vals have similar sounding
variants and large blocks of code do unrelated things that require us
to scroll a lot. I tried breaking them out a bit and clear up naming but
this is far from perfect and we may want to invest more into cleaning
this up. Especially as we add new functionality we should be strict
about not further bloating this method.

Bug: 376659778
Test: REFACTOR_ONLY
Flag: com.android.systemui.scene_container
Change-Id: I9737404e16073b2c81e3474c230c708ce2a7c814