Flagging: wrap injected flag usage

Provide macro to use injected flag while not having to deal with floss not
supporting it.
Usage is like follow:
      #include <android_bluetooth_flags.h>

      const PROVIDER_TYPE& mProvider

      Foo(PROVIDER_TYPE& provider) {
          mProvider = provider
      }

      if (IS_ENABLED(provider, myInjectedFlags)) {
          // new code
      }

Bug: 309697497
Fix: 309697497
Test: m Bluetooth | build change does not impact device code
Change-Id: I48e0b7bfd36fd3103bd3f1ef39d7864757dc7d44