ddl: Ignore FULLTEXT KEYs in CREATE/ALTER TABLE statements

[kolbe]

What problem does this PR solve?

Fixes #3658

What is changed and how it works?

FULLTEXT KEY in CREATE TABLE and ALTER TABLE are ignored.

Check List

Tests

• Integration test
  Tests for CREATE TABLE and ALTER TABLE added to ddl/db_integration_test.go.

Code changes

• Has exported function/method change
  No
• Has exported variable/fields change
  No
• Has interface methods change
  No
• Has persistent data change
  No

Side effects

• Possible performance regression
  No
• Increased code complexity
  No
• Breaking backward compatibility
  No (except that valid MySQL syntax that used to generate an error is now accepted!)

Related changes

• Need to cherry-pick to the release branch
  No
• Need to update the documentation
  No
• Need to update the tidb-ansible repository
  No
• Need to be included in the release note
  Probably no

[codecov]

Codecov Report

Merging #9821 into master will increase coverage by 0.068%.
The diff coverage is 87.5%.

@@               Coverage Diff               @@
##             master      #9821       +/-   ##
===============================================
+ Coverage   78.0515%   78.1195%   +0.068%     
===============================================
  Files           405        405               
  Lines         82156      82014      -142     
===============================================
- Hits          64124      64069       -55     
+ Misses        13330      13244       -86     
+ Partials       4702       4701        -1

[morgo]

LGTM

LGTM

[morgo]

@winkyao PTAL

[morgo]

@kolbe please resolve conflicts

[kolbe]

@kolbe please resolve conflicts

Done.

[winkyao]

LGTM

[morgo]

The CI failed on what looks like an unrelated issue:

----------------------------------------------------------------------
FAIL: db_partition_test.go:1116: testIntegrationSuite.TestPartitionCancelAddIndex

db_partition_test.go:1156:
    c.Assert(err, NotNil)
... value = nil

[morgo]

/run-all-tests

[kolbe]

/run-all-tests tidb-test=pr/772

[winkyao]

@crazycs520 Please help Kolbe to fix the ci.

[crazycs520]

LGTM