LeAudioTestApp: Basic broadcast metadata handling

Uses broadcast metadata list rather than playback state map
for filling in the RecycleViewAdapter items for broadcast list.
This should properly handle Broadcast Scan Assistant use case,
while the previously used playback state was known only for
local broadcasts in the Broadcast Source use case.

Bug: 150670922
Tag: #feature
Test: build
Sponsor: jpawlowski@
Change-Id: Ibda1889e315204b0fd589da42369dace778d2093