1. Add a one-way (encoding-only/fromUnicode) mapping for U+2212 to
   Shift_JIS, EUC-JP and ISO-2022-JP. The last just uses Shift_JIS.

   See https://www.w3.org/Bugs/Public/show_bug.cgi?id=28661

2. Make GBK aliases list compliant to the encoding spec.

3. Add "xA3xA0 => U+3000" to the GBK (windows-936)  and gb18030. This makes it possible to remove the corresponding override in Blink

4. Modify the following to GBK (windows-936). See [1]
  - Add U+01F9 <=> \xA8\xBF
  - Drop U+E7C8 <=> \xA8\xBF

5. The following change is put on hold (NOT included in the CL)  until the resolution of [1]

  - Add U+1E3F <=> \xA8\xBC
  - Drop U+E7C7 <=> \xA8\xBC

The corresponding Blink CL is https://codereview.chromium.org/1167523003/

[1] https://www.w3.org/Bugs/Public/show_bug.cgi?id=28740#c3

BUG=425417,493824
TEST=Once ICU is rolled to this CL, Blink layout test fast/encoding/*.
R=jsbell@chromium.org

Review URL: https://codereview.chromium.org/1162723008