expression: throw "too big precision" error for CAST(AS TIME)

[zz-jason]

What problem does this PR solve?

For the following SQL:

SELECT CAST(1 AS TIME(31));

we should return a error as MySQL does:

MySQL(localhost:3306) > SELECT CAST(1 AS TIME(31));
ERROR 1426 (42000): Too-big precision 31 specified for 'CAST'. Maximum is 6.

Another tiny bugfix is, for cast decimal as time, when the input decimal is NULL, we should return NULL.

What is changed and how it works?

Check the target precision first, if the check result is positive, we then continue to recursively evaluate child expression.

Check List

Tests

• Unit test

Code changes

• Has exported function/method change

Related changes

• Need to cherry-pick to the release branch
• Need to be included in the release note

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This change is 

[XuHuaiyu]

LGTM

[lysu]

/run-all-tests tidb-test=pr/711

[lysu]

/run-all-tests

[codecov-io]

Codecov Report

Merging #8907 into master will increase coverage by 0.03%.
The diff coverage is 55.55%.

@@            Coverage Diff             @@
##           master    #8907      +/-   ##
==========================================
+ Coverage   67.55%   67.58%   +0.03%     
==========================================
  Files         363      363              
  Lines       75301    75309       +8     
==========================================
+ Hits        50868    50901      +33     
+ Misses      19940    19917      -23     
+ Partials     4493     4491       -2

Impacted Files	Coverage Δ
planner/core/errors.go	100% <100%> (ø)	⬆️
expression/builtin_cast.go	79.98% <100%> (+2.54%)	⬆️
planner/core/expression_rewriter.go	67.08% <42.85%> (-0.18%)	⬇️
executor/join.go	77.89% <0%> (-0.41%)	⬇️
expression/distsql_builtin.go	28.05% <0%> (+0.36%)	⬆️
store/tikv/lock_resolver.go	42.65% <0%> (+0.94%)	⬆️

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[lonng]

/run-all-tests

[eurekaka]

LGTM