Inline MODES_API flag

Mostly mechanical changes, except:
* Fixed bug in updateZenRulesOnLocaleChange() - was checking wrong field for FIELD_NAME flag.
* Renamed areChannelsBypassingDnd to hasPriorityChannels, except when it's the "real" areChannelsBypassingDnd, i.e. hasPriorityChannels && allowPriorityChannels.
* Deleted or inlined a handful of methods.

Bug: 310620812
Test: Preexisting + ZenModeHelperTest
Flag: EXEMPT Inlining flag
Change-Id: Icdb8f7abe80b87e468372cfbfe6e51a0dadba3a2