Allow querying for interval from its local reference endpoint

[Abe27342]

This adds an API to @fluidframework/sequence which enables recovering an interval from one of its endpoints. The specific API retrieves the label for the interval collection that endpoint is a part of, as well as the id of the interval. This required storing an additional prop on each endpoint reference. I also fixed a bug in treating the label field differently on reloaded intervals.

The motivation for this change is to enable reasonable undo-redo behaviors for SlideOnRemove intervals to be implementable. There is some discussion of the issue on #11269.

This includes the changes to interval collections from #11550 without suggesting exact implementation for undo-redo.

[msfluid-bot]

⯅ @fluid-example/bundle-size-tests: +330 Bytes

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	392.28 KB	392.45 KB	⯅ +165 Bytes
connectionState.js	680 Bytes	680 Bytes	■ No change
containerRuntime.js	191.92 KB	191.92 KB	■ No change
loader.js	151.12 KB	151.12 KB	■ No change
map.js	42.63 KB	42.63 KB	■ No change
matrix.js	131.63 KB	131.63 KB	■ No change
odspDriver.js	150.23 KB	150.23 KB	■ No change
odspPrefetchSnapshot.js	38.39 KB	38.39 KB	■ No change
sharedString.js	152.26 KB	152.42 KB	⯅ +165 Bytes
Total Size	1.25 MB	1.25 MB	⯅ +330 Bytes

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Baseline commit: a320268

Generated by 🚫 dangerJS against 4ca3956

[anthony-murphy]

i assume we need this because it's not possible to get back to the collection from a specific interval? seems like something that could be improved.

[github-actions]

This commit is queued for merging with the next branch! Please ignore this PR for now. Contact @microsoft/fluid-cr-infra for help.