chore: convert escape-html package to typescript

[jpstevens]

What?

This PR converts the escape-html package to TypeScript.

Why?

Ensures package is fully type checked.

How?

• converted files to .ts
• explicitly type functions and incorrectly-implied variables, based on @type, @param and @return comments

Testing Instructions

• npm run test:unit -- packages/escape-html tests pass
• npm run build:package-types returns a zero exit code

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