improvement(client-presence): attendee connection related unit tests

[WillieHabi]

Description

Added and edited existing attendee connection unit tests.

Moved attendeeDisconnected cases to start under 'already known' as we can't disconnect things we don't know about.

Retitled describe and it blocks so tests read like sentences

[msfluid-bot]

Code Coverage Summary

↑ packages.framework.presence.src:
Line Coverage Change: 0.09%    Branch Coverage Change: 1.84%

Metric Name	Baseline coverage	PR coverage	Coverage Diff
Branch Coverage	83.87%	85.71%	↑ 1.84%
Line Coverage	61.93%	62.02%	↑ 0.09%

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Baseline commit: 522f76f
Baseline build: 303346
Happy Coding!!

Code coverage comparison check passed!!

[msfluid-bot]

⯅ @fluid-example/bundle-size-tests: +245 Bytes

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	464.62 KB	464.65 KB	⯅ +35 Bytes
azureClient.js	562.79 KB	562.83 KB	⯅ +49 Bytes
connectionState.js	724 Bytes	724 Bytes	■ No change
containerRuntime.js	262.21 KB	262.22 KB	⯅ +14 Bytes
fluidFramework.js	406.75 KB	406.77 KB	⯅ +14 Bytes
loader.js	134.17 KB	134.18 KB	⯅ +14 Bytes
map.js	42.71 KB	42.71 KB	⯅ +7 Bytes
matrix.js	148.54 KB	148.54 KB	⯅ +7 Bytes
odspClient.js	528.73 KB	528.78 KB	⯅ +49 Bytes
odspDriver.js	97.84 KB	97.86 KB	⯅ +21 Bytes
odspPrefetchSnapshot.js	42.81 KB	42.82 KB	⯅ +14 Bytes
sharedString.js	164.73 KB	164.74 KB	⯅ +7 Bytes
sharedTree.js	397.21 KB	397.22 KB	⯅ +7 Bytes
Total Size	3.33 MB	3.33 MB	⯅ +245 Bytes

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Baseline commit: 522f76f

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