test(client): fix Signals test

[jason-ha]

to keep test failures from closing connection and sending a telemetry report

Keep test assertions on the side and re-raise outside of signal processing.

Additionally, reorganize code to reduce duplication and tidy some error messages and constant values.

[msfluid-bot]

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

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	460.43 KB	460.47 KB	⯅ +35 Bytes
azureClient.js	559.03 KB	559.08 KB	⯅ +49 Bytes
connectionState.js	680 Bytes	680 Bytes	■ No change
containerRuntime.js	261.68 KB	261.69 KB	⯅ +14 Bytes
fluidFramework.js	402.58 KB	402.6 KB	⯅ +14 Bytes
loader.js	134.17 KB	134.19 KB	⯅ +14 Bytes
map.js	42.43 KB	42.44 KB	⯅ +7 Bytes
matrix.js	145.87 KB	145.88 KB	⯅ +7 Bytes
odspClient.js	526.18 KB	526.23 KB	⯅ +49 Bytes
odspDriver.js	97.8 KB	97.82 KB	⯅ +21 Bytes
odspPrefetchSnapshot.js	42.76 KB	42.78 KB	⯅ +14 Bytes
sharedString.js	162.83 KB	162.84 KB	⯅ +7 Bytes
sharedTree.js	393.05 KB	393.05 KB	⯅ +7 Bytes
Total Size	3.3 MB	3.3 MB	⯅ +245 Bytes

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Baseline commit: 1d2fe12

Generated by 🚫 dangerJS against ef6902a