expression: fix behavior for builtin 'LTrim', 'RTrim' and 'Trim'

[spongedu]

What have you changed? (mandatory)

In TiDB, Builtin LTrim, RTrim and Trim act differently with MySQL. In MySQL, \r\n\t are not trimed but TiDB do:
In MySQL:

mysql> select character_length(rtrim("bar\n     "));
+---------------------------------------+
| character_length(rtrim("bar\n     ")) |
+---------------------------------------+
|                                     4 |
+---------------------------------------+
1 row in set (0.00 sec)

mysql> select character_length(ltrim("\r  bar"));
+------------------------------------+
| character_length(ltrim("\r  bar")) |
+------------------------------------+
|                                  6 |
+------------------------------------+
1 row in set (0.00 sec)

mysql> select character_length(trim("\r  bar\n"));
+-------------------------------------+
| character_length(trim("\r  bar\n")) |
+-------------------------------------+
|                                   7 |
+-------------------------------------+
1 row in set (0.00 sec)

In TiDB:

tidb> select character_length(rtrim("bar\n     "));
+---------------------------------------+
| character_length(rtrim("bar\n     ")) |
+---------------------------------------+
|                                     3 |
+---------------------------------------+
1 row in set (0.01 sec)

tidb> select character_length(ltrim("\r  bar"));
+------------------------------------+
| character_length(ltrim("\r  bar")) |
+------------------------------------+
|                                  3 |
+------------------------------------+
1 row in set (0.00 sec)

tidb> select character_length(trim("\r  bar\n"));
+-------------------------------------+
| character_length(trim("\r  bar\n")) |
+-------------------------------------+
|                                   3 |
+-------------------------------------+
1 row in set (0.00 sec)

What is the type of the changes? (mandatory)

Compatibility

How has this PR been tested? (mandatory)

Add some unittests and integration tests

Does this PR affect documentation (docs/docs-cn) update? (mandatory)

Does this PR affect tidb-ansible update? (mandatory)

Does this PR need to be added to the release notes? (mandatory)

Refer to a related PR or issue link (optional)

Benchmark result if necessary (optional)

Add a few positive/negative examples (optional)

[zz-jason]

LGTM

Reviewable status: 0 of 3 files reviewed, all discussions resolved

[zz-jason]

Reviewable status: 0 of 3 files reviewed, all discussions resolved

[zz-jason]

/run-all-tests

[coocood]

LGTM

[tiancaiamao]

/run-all-tests