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	457.66 KB	457.66 KB	■ No change
azureClient.js	558.43 KB	558.43 KB	■ No change
connectionState.js	680 Bytes	680 Bytes	■ No change
containerRuntime.js	260.13 KB	260.13 KB	■ No change
fluidFramework.js	369.52 KB	369.6 KB	⯅ +82 Bytes
loader.js	135.12 KB	135.12 KB	■ No change
map.js	39.83 KB	39.83 KB	■ No change
matrix.js	142.48 KB	142.48 KB	■ No change
odspClient.js	526.33 KB	526.33 KB	■ No change
odspDriver.js	98.29 KB	98.29 KB	■ No change
odspPrefetchSnapshot.js	42.11 KB	42.11 KB	■ No change
sharedString.js	159.28 KB	159.28 KB	■ No change
sharedTree.js	369.51 KB	369.59 KB	⯅ +82 Bytes
Total Size	3.23 MB	3.23 MB	⯅ +164 Bytes

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Baseline commit: c670468

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