Prevent Media notification spam from spiking SystemUI memory use

If an app spams Media Notifications it can lead to massive increase to memory use, since the waiting loadMediaData jobs will be waiting on the background executor looper to be processed. This is especially problematic if there are other tasks taking the thread.

This CL:
- Moves media actions code to MediaActions.kt so it can be reused in new MediaDataLoader class
- Duplicates `loadMediaData` and `loadMediaDataForResumption` calls in `MediaDataLoader`
- Implements logic which cancels in-flight media data load requests for same sbn/key if an update comes in.

Bug: 358350077
Flag: com.android.systemui.media_load_metadata_via_media_data_loader
Test: atest LegacyMediaDataManagerImplTest MediaDataLoaderTest + device testing
Change-Id: Ic29b6954c4cd3489751fafc1c8a8b92a7a2016de