refactor(tree): use SharedTree format version 3 by default

[yann-achard-MS]

Description

Makes SharedTreeFormatVersion.v3 the default value.

Breaking Changes

This is a breaking change in the sense that it breaks collaboration with versions of SharedTree before v3 format was implemented (i.e. anything rc-3 and earlier).

We are leveraging the fact that SharedTree doesn't yet have as strong of compatibility guarantees as other DDSes with current production usage.

[msfluid-bot]

⯅ @fluid-example/bundle-size-tests: +164 Bytes

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	453.98 KB	453.98 KB	■ No change
azureClient.js	551.23 KB	551.23 KB	■ No change
connectionState.js	680 Bytes	680 Bytes	■ No change
containerRuntime.js	257.82 KB	257.82 KB	■ No change
fluidFramework.js	356.74 KB	356.82 KB	⯅ +82 Bytes
loader.js	132.91 KB	132.91 KB	■ No change
map.js	41.45 KB	41.45 KB	■ No change
matrix.js	143.67 KB	143.67 KB	■ No change
odspClient.js	519.76 KB	519.76 KB	■ No change
odspDriver.js	97.29 KB	97.29 KB	■ No change
odspPrefetchSnapshot.js	42.15 KB	42.15 KB	■ No change
sharedString.js	160.19 KB	160.19 KB	■ No change
sharedTree.js	356.73 KB	356.81 KB	⯅ +82 Bytes
Total Size	3.19 MB	3.19 MB	⯅ +164 Bytes

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Baseline commit: 3eb328b

Generated by 🚫 dangerJS against 94cee4b