Fix incorrect tuple usage and syntax

[sandersn]

Lots of packages use singleton tuple syntax in place of array syntax. [number] was previously almost compatible with number[], so it slipped through in a lot of places. Now, with fixed-length tuples, this reliably fails.

The fixed-length tuple also found a couple of errors, in highchart and leaflet. I changed the highchart test to be correctly-typed, although the intent of the test is probably a bit changed. I am 99% sure the test is wrong, though, based on the highchart documentation.

The leaflet test assumes that LatLng marks whether altitude was provided in its type, which it does not, so converting a LatLng returns [number, number] | [number, number, number], which was previously equivalent to [number, number].

It's relatively simple to add a type parameter LatLng<T extends number | undefined>, but it's a big change that's outside the scope of this set of simple fixes.

[dt-bot]

types/aws-lambda/index.d.ts

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types/fingerprintjs2/index.d.ts

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types/heredatalens/index.d.ts

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types/highcharts/index.d.ts

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types/validate.js/index.d.ts

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types/xml2js/index.d.ts

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[ghost]

Rebase against master to fix test failures. (#21384)