Encodings: Migrate tests dependent on WPT resource to wpt_internal

One test in fast/encoding/api reached into WPT to grab a resource file
(a canonical list of encodings/labels), which caused problems for the
auto-roller. Other tests relied on an out-of-date copy of the file.

Migrate the tests to wpt_internal/encoding and use the WPT version of
the file. Also convert the files from .html to window.js and fix an
ISO-2022-JP escaping test.

Bug: 1079403
Change-Id: I27495779d8275e3f13bcfbf8b9b3b2bc443542ca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2194940
Commit-Queue: Joshua Bell <jsbell@chromium.org>
Commit-Queue: Robert Ma <robertma@chromium.org>
Auto-Submit: Joshua Bell <jsbell@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#767581}