Make ISO-2022-JP converter compliant to the WHATWG encoding spec

The encoding of 373 code point into ISO-2022-JP failed because they're
mapped to SJIS code points for which there's no JIS 208 mapping.
Using JIS X 208 table in EUC-JP solves this issue.

Upstream bug: https://unicode-org.atlassian.net/browse/ICU-20251

Bug: 901255
Test: https://www.w3.org/International/tests/repo/run?base=encoding&batch=encoding-dbl-byte&test=legacy-mb-japanese/iso-2022-jp/iso2022jp-encode-form.html
Change-Id: I3237fa1269a3ae2e89b22e246aaf2ae43fd56c7d
Reviewed-on: https://chromium-review.googlesource.com/c/1314052


Reviewed-by: Joshua Bell <jsbell@chromium.org>