New eslint fixes

[bdemann]

This adds fixes for 10 of the offending eslint rules reducing us down to only 7 tech-debt disabled rules.

Add 9 additional rules that were easy to fix and seem like they would be good.

• func style (function should be declarations not declarations)
• array-callback-return (map, filter, reduce, etc, should have returns (thus avoiding undefined[])
• no-template-curly-in-string (to avoid accidentally doing "This is ${myValue}" instead of This is ${myValue}
• eqeqeq (enforcing === instead of == and !== instead of !=)
• prefer-template (use template literal instead of string concat)
• no-param-reassign
• @typescript-eslint/prefer-for-of
• prefer-arrow-callback
• no-var

Caution

Change the base of this PR to main before merging and merge #1734 first.