Match the spec's "find the IPv6 address compressed piece index"

The spec's algorithm is based on ours, but the algorithm and variable names changed, so let's align.

Follows whatwg/url@7ff8de0.

README.md

@@ -4,7 +4,7 @@ whatwg-url is a full implementation of the WHATWG [URL Standard](https://url.spe
 
 ## Specification conformance
 
-whatwg-url is currently up to date with the URL spec up to commit [302c5af](https://github.com/whatwg/url/commit/302c5afb376b7fb1d5943634ad6c3a2e71c37f37).
+whatwg-url is currently up to date with the URL spec up to commit [da212c9](https://github.com/whatwg/url/commit/da212c98f0bba9c35aec3728bbcc13f8f3a7eb52).
 
 For `file:` URLs, whose [origin is left unspecified](https://url.spec.whatwg.org/#concept-url-origin), whatwg-url chooses to use a new opaque origin (which serializes to `"null"`).
 

lib/url-state-machine.js

@@ -298,7 +298,7 @@ function parseIPv6(input) {
 
 function serializeIPv6(address) {
   let output = "";
-  const compress = findLongestZeroSequence(address);
+  const compress = findTheIPv6AddressCompressedPieceIndex(address);
   let ignore0 = false;
 
   for (let pieceIndex = 0; pieceIndex <= 7; ++pieceIndex) {
@@ -384,35 +384,34 @@ function parseOpaqueHost(input) {
   return utf8PercentEncodeString(input, isC0ControlPercentEncode);
 }
 
-function findLongestZeroSequence(arr) {
-  let maxIdx = null;
-  let maxLen = 1; // only find elements > 1
-  let currStart = null;
-  let currLen = 0;
-
-  for (let i = 0; i < arr.length; ++i) {
-    if (arr[i] !== 0) {
-      if (currLen > maxLen) {
-        maxIdx = currStart;
-        maxLen = currLen;
+function findTheIPv6AddressCompressedPieceIndex(address) {
+  let longestIndex = null;
+  let longestSize = 1; // only find elements > 1
+  let foundIndex = null;
+  let foundSize = 0;
+
+  for (let pieceIndex = 0; pieceIndex < address.length; ++pieceIndex) {
+    if (address[pieceIndex] !== 0) {
+      if (foundSize > longestSize) {
+        longestIndex = foundIndex;
+        longestSize = foundSize;
       }
 
-      currStart = null;
-      currLen = 0;
+      foundIndex = null;
+      foundSize = 0;
     } else {
-      if (currStart === null) {
-        currStart = i;
+      if (foundIndex === null) {
+        foundIndex = pieceIndex;
       }
-      ++currLen;
+      ++foundSize;
     }
   }
 
-  // if trailing zeros
-  if (currLen > maxLen) {
-    return currStart;
+  if (foundSize > longestSize) {
+    return foundIndex;
   }
 
-  return maxIdx;
+  return longestIndex;
 }
 
 function serializeHost(host) {