Convert SettingsProxy and UserSettingsProxy to Kotlin.

Conversion to Kotlin is the first step towards migrating
register/unregister content observer APIs to background thread.

Test: atest / manual flash
Bug: 330299944
Flag: NONE Java to Kotlin migration, flag not needed.
Change-Id: I793d4bd9ad3d6ac9e39c3e97b7e4edc5b794ba84
9 files changed