[js_runtime, corelib] Use `URLSearchParams` for computing `Uri.query` string.

[rakudrama]

Customer experiments show that it is considerably (>10x) faster to use the browser's URLSearchParams to compute the query string from the queryParameters map when the map contains large values that require some escaping (e.g. 500K of JSON).

Uri should be slightly refactored to allow the platform libraries to implement the entire parameter string generation.
The web implementation would use URLSearchParams is it is available.
Some care will be needed to verify that the escaping matches exactly and the error handling (e.g. singleton surrogates) is the same.

[nshahan]

@rakudrama Do you have more work planned here? OK to close this issue?

[rakudrama]

@nshahan I want it to clear 1P first, possibly with an experiment to remove the work-around so that this approach is fully validated.