During GC init, fail fast if there's an unrecognized Test Mode in effect

[markfields]

See this comment in a PR I had to abandon for now (will revisit in 2 weeks).

[msfluid-bot]

⯅ @fluid-example/bundle-size-tests: +241 Bytes

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	387.39 KB	387.51 KB	⯅ +121 Bytes
connectionState.js	680 Bytes	680 Bytes	■ No change
containerRuntime.js	191.5 KB	191.62 KB	⯅ +120 Bytes
loader.js	149.91 KB	149.91 KB	■ No change
map.js	42.67 KB	42.67 KB	■ No change
matrix.js	127.15 KB	127.15 KB	■ No change
odspDriver.js	149.26 KB	149.26 KB	■ No change
odspPrefetchSnapshot.js	38.31 KB	38.31 KB	■ No change
sharedString.js	147.79 KB	147.79 KB	■ No change
Total Size	1.24 MB	1.24 MB	⯅ +241 Bytes

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Baseline commit: 4beded1d7847e3bbc965a329c6eed36b2da82f9d

Generated by :no_entry_sign: dangerJS against ea757a39e6363d06d880143bb2548d77de3d773e

[markfields]

We haven't come back around to this, seems like consensus was it's too aggressive of a stance. So when we start shrinking sweep timeout for testing (specifically after PR #12044) we will have to be careful about opening the same document in old code (which will have sweep timeout at least as long as the 1 day buffer) v. new code which can be very short. Likewise if you open a document with/without TestOverride.DisableSnapshotCache setting (which toggles snapshotCacheExpiry number between 0 and 2 days)