Adjust withContext usage for SettingsProxy

 - Only call withContext if current dispatcher is different than the
   one used by settings. This will reduce overhead of calling
   withContext when changing contexts is not needed.

 - Remove deprecated nameCoroutine() call, which was not performing
   tracing correctly.

Bug: 289353932
Bug: 330299944
Test: atest SystemUITests
Flag: EXEMPT refactor
Change-Id: Id836fd952ebde4473847cc5433ce7f1ca0615c7d