1. Update ucmlocal.mk and convertrs.txt to refer to euc-kr-html.ucm
instead of windows-949.ucm

2. Tighten up the valid code range for the following converters:

   EUC-KR, Shift_JIS, Big5

This is to add back an ASCII range byte to the stream per
the encoding spec when they're either illegal as a 'trail byte' or
there's no assigned code point for a "lead + trail" sequence.
For instance, with this change, '0xF3 0x41' in EUC-KR is converted to
'U+FFFD U+0041' instead of 'U+FFFD'.

This change requires adding 2 ~ 8 new states to the conversion
table of each converter mentioned above leading to 6.5kB net increase
in the final data size.

3. Tighten the trail byte range for 2-byte sequences starting with 0x8E
from [A1,E2] to [A1,DF] in EUC-JP and update the corresponding generating
script.

4. Change the substitution characters for EUC-JP and Shift_JIS to
match other converters. i.e. make them produce U+FFFD when encountering
an invalid input. Before this chaange, they emitted U+001A.

5. Enable 'U_CHARSET_IS_UTF8' configuration flag.
Chromium/Blink does not rely on ICU for the code conversion between
the 'system native encoding' (if it's one of legacy encodings)
and Unicode. With this configuration, we can cut down the code size
a bit.

6. Update the icudtl.dat (all platforms) and assembly files (mac,linux)
   and the icudata dll (windows)

See https://codereview.chromium.org/1026453002 for a new blink test
added ( fast/encoding/char-decoding-invalid-trail.html )

BUG=450312,430823
TEST=Blink: fast/encoding/char-decoding-{truncated,invalid-trail}.html
TEST=base_unittests --gtest_filter=*Conv*, browser_tests --gtest_filter=*ncoding*
R=jsbell@chromium.org, mark@chromium.org

Review URL: https://codereview.chromium.org/984233002

A. Converter update per HTML encoding spec along with changes in
  the encoding name alias table.
B. Remove all the codes for converters Blink and Chromium do not need
(SCSU, Lotus, ISO-2022-xx other than JP, BOCU, UTF-7, etc).

This is reapplying the following CLs (that we used for ICU 52.1) to ICU 54.1 :

https://codereview.chromium.org/598383002
https://codereview.chromium.org/654153002

We have two upstream bugs filed for A and B above:
  http://www.icu-project.org/trac/ticket/11296
  http://www.icu-project.org/trac/ticket/10303

In addiition to A and B, we unified Big5 and Big5-HKSCS per
the encoding spec (bug 277868). That also includes properly supporting
the four 2-character sequences ( see http://crbug.com/277868#c3 ).
big5_gen.sh deviates from the current spec to work around a bug
in the spec. (see https://www.w3.org/Bugs/Public/show_bug.cgi?id=27878)

Moreover, ucmlocal.mk is added to list only encodings we want to support.

Also, tighten the state table for windows-946-2000.ucm that we use
for EUC-KR for now. And, drop 'base' map for windows-{936,949}-2000.ucm.

Finally, add euc-kr-html.ucm along with scripts/euckr_gen.sh, but
it is not yet used pending the resolution of bug 450312.

Data size checkpoint: 20,566,864 bytes (the original ICU 54=25,343,024)

BUG=277868, 428145, 450312
TEST=net_unittests --gtest_filter="*ilenameUtil*"
TEST=base_unittests --gtest_filter="*Conv*"
TEST=browser_tests --gtest_filter="*ncoding*"
TEST=Blink: fast/encoding/*
R=jsbell@chromium.org, mark@chromium.org

Review URL: https://codereview.chromium.org/839713003