JS: update externs from closure-compiler

[erik-krogh]

NOTE: Still in progress.

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Inspired by this anomalous result, which is fixed by this PR.

Reviewing this PR is hard, so I'll explain how it was created.

I went through our externs and updated all the files that originated from closure-compiler to their latest version.

Started by copy-pasting the externs/browser folder from closure-compiler into our externs/web.
I didn't update the nodejs folder, as the externs I found in closure-compiler were not structured in the same way, which gave FPs in some queries.

Then I went through all the externs that had not been touched, and updated the ones from closure-compiler to their latest version.

This means that the contrib/externs folder from closure-compiler has not been copy-pasted into our externs.

There are a few files that have been moved/deleted:

• fileapi.js has been renamed to nonstandard_fileapi.js.
• The intl.js file was duplicated between the web and es folder. I left the one in es.
• w3c_encoding.js was duplicate of whatwg_encoding.js. I've left the latter.

TODO:

• very large evaluation
• change note?