Live beacons: track users live beacons

[kerryarchibald]

matrix-org/matrix-spec-proposals#3489

Done:

• Send m.beacon_info.* state events.
• track m.beacon_info.* events in room state
• expose and maintain 'user room has live beacons' property in room state
• add ability to monitor liveness of beacon

In this PR:

• get users own beacons from room state, monitor liveness
• maintain 'user has live beacons' property)

In next PRs:

• get users own beacons from room state, monitor liveness and show live state
• produce good unique suffixes for beacon info events
• geolocate and send m.beacon events for live beacons
• maintain liveness state of beacons (checking for expiry, flipping isLive on event content)

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This change is marked as an internal change (Task), so will not be included in the changelog.

Preview: https://pr8061--matrix-react-sdk.netlify.app
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[codecov]

Codecov Report

Merging #8061 (20c5ed9) into develop (e677901) will increase coverage by 0.08%.
The diff coverage is 98.46%.

@@             Coverage Diff             @@
##           develop    #8061      +/-   ##
===========================================
+ Coverage    27.02%   27.11%   +0.08%     
===========================================
  Files          866      867       +1     
  Lines        52015    52080      +65     
  Branches     13185    13192       +7     
===========================================
+ Hits         14055    14119      +64     
- Misses       37960    37961       +1     

Impacted Files	Coverage Δ
src/stores/OwnBeaconStore.ts	98.46% <98.46%> (ø)

[dbkr]

lgtm, tests look thorough too - thanks!