fix(dts/ffi): non-exact types break FFI inference

[sno2]

Closes #14963

Notes:

• The tuple item mapping method is more efficient than recursion and supports as many iterations as a union can have: ~50,000 parameters instead of the 1,000 that regular tail-end recursion optimized (which the other implementation was not) generics.
• The FooMap and Foo<Key> method was previously encouraged by Ryan Kavanaugh and it allows TypeScript to inline some types and for composition between things that may want to also check if something is Foo via FooMap.

[sno2]

I'm not sure how to run the linter on the file. It passes deno lint but CI seems to be failing.

[aapoalas]

Lint can be run using eg.

deno run --unstable --allow-run=git,./third_party/prebuilt/linux64/dlint,cargo --allow-read=./ --allow-write=./ ./tools/lint.js --check

Aside from that, the tests should be moved to the dedicated test file, FromNativeTypeMap needs to be fixed and some changes seem unnecessary though I don't know for sure.

[littledivy]

LGTM