Don't decode arbitrary %2e during URL parsing after all

[annevk]

This reverts commit 47d2089.

See whatwg/url#87 for discussion.

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This change is 

[wpt-pr-bot]

Reviewers for this pull request are: @Sebmaster, @domenic, @frewsxcv, @mikewest, @rubys, @sideshowbarker, @smola, @tomalec, @xiaojunwu, and @zcorpan.

[annevk]

Note that Firefox already WONTFIXED their corresponding bug (and therefore agrees with this change) and Safari advocated for it. We don't really know what the other browsers will do unfortunately.

[annevk]

I suggest we keep this open for now given that Google is not okay with going in this direction.

[annevk]

I suggest we land this per whatwg/url#87 (comment) since what's currently defined isn't really implemented anywhere.

[domenic]

After updating whatwg-url per https://github.com/whatwg/url/pull/156/files the following tests additionally fail:

  1) Web platform tests setters pathname <view-source+http://example.net/home?lang=fr#nav>.pathname = "\a\%2E\b\%2e.\c" \ is *not* a segment delimiter for non-'special' URLs:

      AssertionError: 'view-source+http://example.net/\\a\\%2E\\b\\%2e.\\c?lang=fr#nav' == 'view-source+http://example.net/\\a\\.\\b\\..\\c?lang=fr#nav'
      + expected - actual

      -view-source+http://example.net/\a\%2E\b\%2e.\c?lang=fr#nav
      +view-source+http://example.net/\a\.\b\..\c?lang=fr#nav

  2) Web platform tests setters pathname <http://example.net>.pathname = "%2e%2E%c3%89té" Bytes already percent-encoded are left as-is, except %2E.:

      AssertionError: 'http://example.net/%2e%2E%c3%89t%C3%A9' == 'http://example.net/..%c3%89t%C3%A9'
      + expected - actual

      -http://example.net/%2e%2E%c3%89t%C3%A9
      +http://example.net/..%c3%89t%C3%A9