support gbk charset

[spongedu]

1. Support charset gbk in parser;
2. fix description for charsetlatin and charsetbin1 and charsetbin

What problem does this PR solve?

We're using parser to develop some our systems and found that charset gbk is not supported yet in parser, which makes some SQL fail to work.
As a MySQL compatible parser, I think we should support gbk as MySQL's parser do, and leave the charset-compatible issues to TiDB layer.

What is changed and how it works?

Add gbk into supported charsets, and add related tests

Check List

Tests

• Unit test
• Manual test

[codecov]

Codecov Report

Merging #808 into master will decrease coverage by 0.08%.
The diff coverage is n/a.

@@ Coverage Diff @@## master #808 +/- ##
==========================================
- Coverage 78.35% 78.27% -0.09% 
==========================================
Files 40 40 Lines 14773 14707 -66 ==========================================
- Hits 11576 11512 -64 - Misses 2509 2515 +6 + Partials 688 680 -8 

[kennytm]

Rest LGTM.

Why do we support GBK rather than its superset GB18030?

[spongedu]

Rest LGTM.

Why do we support GBK rather than its superset GB18030?

@kennytm Because we just met gbk in our cases. maybe gb18030 should be supported as well

[tiancaiamao]

PTAL @bb7133@wjhuang2016

[wjhuang2016]

GetSupportedCharsets need to change too.

[spongedu]

@wjhuang2016 PTAL :)

[ti-chi-bot]

@spongedu: PR needs rebase.

Details

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.27%. Comparing base (8be0c27) to head (824320b).
⚠️ Report is 255 commits behind head on master.

⚠️Current head 824320b differs from pull request most recent head 73b534d

Please upload reports for the commit 73b534d to get more accurate results.

Additional details and impacted files

@@ Coverage Diff @@## master #808 +/- ##
==========================================
- Coverage 78.35% 78.27% -0.09% 
==========================================
Files 40 40 Lines 14773 14707 -66 ==========================================
- Hits 11576 11512 -64 - Misses 2509 2515 +6 + Partials 688 680 -8 

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