tree: Cleanup object property tests, and fix bug

[CraigMacomber]

Description

This cleans up a section of the object node tests which used schema types in a complicated generic way that's fragile and hard to work with.

When rewriting these tests, I focused the new ones on testing aspects that actually have special logic and are likely to break instead of just different value types. Thus the tests now cover the odd normalization cases of numbers.

These tests found a couple of issues:

• unhydrated node handling of null was incorrect (see changeset)
• Some type errors were thrown for invalid user input. TO help keep it easy to tell which errors are our bugs and which are app bugs I've made these fluid usage errors.
• A needless check for NaN was included where the check for isFinaite would handle it correctly (Number.isFinite considers NaNs to not be finite: comment already calls out NaN and it has test coverage so this seems like a safe change.)

Reviewer Guidance

The review process is outlined on this wiki page.

[msfluid-bot]

⯅ @fluid-example/bundle-size-tests: +217 Bytes

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	460.31 KB	460.34 KB	⯅ +35 Bytes
azureClient.js	557.29 KB	557.34 KB	⯅ +49 Bytes
connectionState.js	724 Bytes	724 Bytes	■ No change
containerRuntime.js	259.58 KB	259.6 KB	⯅ +14 Bytes
fluidFramework.js	405.95 KB	405.95 KB	■ No change
loader.js	134.34 KB	134.36 KB	⯅ +14 Bytes
map.js	42.46 KB	42.46 KB	⯅ +7 Bytes
matrix.js	148.63 KB	148.64 KB	⯅ +7 Bytes
odspClient.js	524.25 KB	524.3 KB	⯅ +49 Bytes
odspDriver.js	97.84 KB	97.86 KB	⯅ +21 Bytes
odspPrefetchSnapshot.js	42.81 KB	42.82 KB	⯅ +14 Bytes
sharedString.js	164.82 KB	164.83 KB	⯅ +7 Bytes
sharedTree.js	396.41 KB	396.4 KB	⯆ -7 Bytes
Total Size	3.31 MB	3.31 MB	⯅ +217 Bytes

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Baseline commit: 082c72d

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