Support regular JS numbers for incoming 64-bit integers

[RunDevelopment]

fixes #4113

This adds support for regular JS numbers (think typeof x === 'number') as values for u64 and i64 parameters. This should makes Rust APIs taking large numbers more convenient on the JS side and allows bindings for JS functions that return large numbers (e.g. Date.now()).

For details on the number -> bigint conversion, see the doc comment for number_to_bigint. Otherwise, the implementation of this PR is quite simple. The correctness of the conversion is tested in the optional_primitives test.

The reason this PR is still a draft is that I haven't updated the code for function signature types yet. E.g. arg: u64 is still arg: bigint in TS, even thought it should be arg: bigint | number now. I'm waiting for #4188, because #4188 add exactly the functionality I need to implement this.