fix: should not replace literal + with a space in the query string

[macabeus]

This PR fixes #943, in which a literal + from the query string is replaced with a space.

[macabeus]

We don't need to replace %20 with space because we are already calling decodeURIComponent earlier.

[macabeus]

We should replace + with a space before calling decodeURIComponent.
Otherwise, we won't know whether a + comes from a space (and we want to replace it with space) or comes from a %2B (and we want to keep it).

[SaltyAom]

Thanks for the pull request, but I would seconded this.

According to HTML 4.01 specification, section 17.13.4.

application/x-www-form-urlencoded
This is the default content type. Forms submitted with this content type must be
encoded as follows:

1. Control names and values are escaped. Space characters are replaced by ‘+’,
   and then reserved characters are escaped as described in [RFC1738]

By default, an HTML form would be submitted in an application/x-www-form-urlencoded format, which appended data to query parameters for GET request.

This means this PR would break an HTML form parsing functionality.

Although RFC 3986 states that pathname should use %20 for space but leave an interpretation for query parameters (if I understood it correctly)

Furthermore, according to the Web Standard implementation of URLSearchParams which treats + as space.

console.log(new URL("https://saltyaom.com?message=hello+world").searchParams.get("message"))
// hello world

This implied that JavaScript developers would likely expect the implementation of URLSearchParams to be the standard.

So I'm likely going to stick with the current implementation of treating + as a space unless there's a solid counter-argument for my reasoning.