Split api.Headers.lexicographical_sorting in two and update the data

[ddbeck]

Summary

Split two wrongly combined features for iterating over Headers objects and update their support data.

Test results and supporting details

Manually tested with something close to this (extraneous logging and such removed):

var populate = [];
var abc = ["A", "B", "C", "D", "E", "F"].reverse();
for (var index = 0; index < 512; index++) {
  populate[index] = ["X-" + abc[index % abc.length], "_"];
}

var headers = new Headers([
  ["Accept-Language", "en-US,en;q=0.5"],
  ["Accept-Language", "en-US,en;q=0.5"],
  ["Accept-Language", "en-US,en;q=0.5"],
].concat(populate));
console.log(headers);
for (var header of headers) {
  console.log(header);
}

I was investigating this feature in the course of creating a fetch feature in web-features. The data for Safari looked dubious. I soon found out that the two parts of this (sorting and combining) have different histories. Instead of using partial implementations, I split the feature in two.

The highlights here:

• Safari always supported both (from 10.1)
• Edge acquired them separately (in 16 and 18)
• Firefox got both at the same time, but later than reported (57, not 44)

[foolip]

These are some very specific subfeatures, but if we should have them at all I think it's best to split them if they weren't implemented together.