Migrate and update the excess property checking docs

[orta]

Fixes #2240 and #1875

Migrates and does an editing run over the handbook v1 version of the excess property check docs

[github-actions]

Got false positives?

Make changes to the global settings spellcheck.json in /microsoft/TypeScript-Website.

Make changes to this repo's settings in spellcheck.json.

Typos for Object Types.md

Line	Typo
89	says is that if the property is set, it better have a specifi
365	to createSquare is spelled ****colour instead of color.
475	g letters and packages in the U.S.
521	ate we have to write, and for signaling intent that several different
870	readonly property modifier, assignability isn't bidirectional between r
917	We can also [destructure tuples](https://developer.moz
932	to name our variables when we destructure them.
1057	s tend to be created and left un-modified in most code, so annotating t

Typos for Interfaces.md

Line	Typo
13	"duck typing" or "structural subtyping".
111	## Readonly properties
189	to createSquare is spelled ****colour instead of color.
676	When interacting with 3rd-party JavaScript, you may need to u

Generated by 🚫 dangerJS against 82513b4

[MichaelAllenWarner]

The lack of documentation for excess-property checks in the v2 handbook seems like a glaring omission. Would be great to see this merged!

As mentioned in #2240, I also think it would be nice to document the fact that excess properties are allowed in object literals if they're spread in with the ... operator.

[github-actions]

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