SystemUI: overheat warning enhancements and bug fixes.

1) Add support of dynamically enabling/disabling overheat warning
   upon Settings change at runtime.
2) Rename related classes, methods, and variables to improve the
   readability.
3) Fix an issue where skin overheat warning fails to show when previous
   dismissal is triggered by intent ACTION_DISMISSED_TEMP_WARNING or
   ACTION_CLICKED_TEMP_WARNING.

Test: atest SystemUITests
Test: enable/disable overheat warning via adb command and trigger the
      warning with emulated temperature.

Bug: 126326427
Bug: 129043751
Change-Id: I844f75a042651bdd433715fedfc190b8fbff0fd4