feat(tree): Add the ability to associate metadata with Node Schema

[Josmithr]

Users of TreeView can now specify metadata when creating Node Schema, via SchemaFactoryAlpha.
This metadata may include system-understood properties like description.

Example:

const schemaFactory = new SchemaFactoryAlpha(...);
class Point extends schemaFactory.object("Point", {
	x: schemaFactory.required(schemaFactory.number),
	y: schemaFactory.required(schemaFactory.number),
},
{
	metadata: {
		description: "A point in 2D space",
	},
}) {}

[Josmithr]

Note: I've added node-level metadata to these schemas, and fixed some typos. But otherwise, most of these changes are whitespace. If you toggle the "Hide whitespace" option in the GitHub UI, these will be easier to review.

[jzaffiro]

Docs look good (pending your TODO)!

[github-actions]

🔗 No broken links found! ✅

Your attention to detail is admirable.

linkcheck output

> [email protected] ci:check-links /home/runner/work/FluidFramework/FluidFramework/docs
> start-server-and-test "npm run serve -- --no-open" 3000 check-links

1: starting server using command "npm run serve -- --no-open"
and when url "[ 'http://127.0.0.1:3000' ]" is responding with HTTP status code 200
running tests using command "npm run check-links"


> [email protected] serve
> docusaurus serve --no-open

[SUCCESS] Serving "build" directory at: http://localhost:3000/

> [email protected] check-links
> linkcheck http://localhost:3000 --skip-file skipped-urls.txt

Crawling...

Stats:
  170142 links
    1596 destination URLs
    1825 URLs ignored
       0 warnings
       0 errors