Instances of split should link to Infra

[GPHemsley]

The "IPv4 parser" and the "application/x-www-form-urlencoded parser" both use the word split without defining the algorithm to do so. In particular, this leaves ambiguous the case where the delimiter does not occur in the string or byte sequence.

Infra defines many different types of splits, but it is likely that the "strictly split" algorithm is what is intended here.

One caveat, however, is that the "application/x-www-form-urlencoded parser" operates on bytes, rather than on code points. This might require some finagling.

[TimothyGu]

See https://github.com/whatwg/url/pull/300/files#diff-03b21320f26423640f89c447968191e5R2381, #300 (comment), whatwg/infra#91

[GPHemsley]

Oh, very good.