parser: fix CHARACTER VARYING syntax

[lauhg]

What problem does this PR solve?

Fix compatibility problem about CHARACTER VARYING syntax

Issue: #410

MySQL Syntax:

type:
...
  | CHAR_SYM field_length opt_charset_with_opt_binary
  | CHAR_SYM opt_charset_with_opt_binary
  | nchar field_length opt_bin_mod
  | nchar opt_bin_mod
  | varchar field_length opt_charset_with_opt_binary
  | nvarchar field_length opt_bin_mod

Bad SQL Case:

create table t (a character varying(1));
create table t (a character varying(255));
create table t (a char varying(255));
create table t (a character);

create table t (a nchar);
create table t (a nchar varchar(50));
create table t (a nchar varying(50));

create table t (a national character varying(50));
create table t (a national char varying(50));

Check List

Tests

• Unit test

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #465 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #465   +/-   ##
=======================================
  Coverage   71.09%   71.09%           
=======================================
  Files          32       32           
  Lines        7534     7534           
=======================================
  Hits         5356     5356           
  Misses       1662     1662           
  Partials      516      516

Impacted Files	Coverage Δ
parser.go	70.58% <ø> (ø)	⬆️
misc.go	96.42% <ø> (ø)	⬆️

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[codecov]

Codecov Report

Merging #465 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #465   +/-   ##
=======================================
  Coverage   71.09%   71.09%           
=======================================
  Files          32       32           
  Lines        7534     7534           
=======================================
  Hits         5356     5356           
  Misses       1662     1662           
  Partials      516      516

Impacted Files	Coverage Δ
parser.go	70.58% <ø> (ø)	⬆️
misc.go	96.42% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1619718...e37a50f. Read the comment docs.

[zier-one]

LGTM

[zier-one]

@tangenta
PTAL

[tangenta]

@lauhg Thank you for your contribution! Please address the comments below.

[tangenta]

LGTM