Account for gaps in the LocalReference array when packing segments

[pleath]

When Zamboni combines TextSegment's, it needs to update LocalReference's that refer to the segments. It wasn't doing this correctly in the case where, say, a reference is found at position 0, then some number of segments without references were appended, then a segment containing a reference was appended. The text corresponding to the segments without references wasn't accounted in the final segment. A gap needs to be introduced in the LocalReference array to make the references correct.

[msfluid-bot]

⯅ @fluid-example/bundle-size-tests: +510 Bytes

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	380.96 KB	381.12 KB	⯅ +170 Bytes
containerRuntime.js	188.25 KB	188.25 KB	■ No change
loader.js	158.72 KB	158.72 KB	■ No change
map.js	203.34 KB	203.34 KB	■ No change
matrix.js	290.68 KB	290.85 KB	⯅ +170 Bytes
odspDriver.js	159.46 KB	159.46 KB	■ No change
odspPrefetchSnapshot.js	46.03 KB	46.03 KB	■ No change
sharedString.js	310.16 KB	310.32 KB	⯅ +170 Bytes
Total Size	1.73 MB	1.73 MB	⯅ +510 Bytes

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Baseline commit: a622b1e

Generated by 🚫 dangerJS against 6c96512