Math func pushdown (#2217)

[ti-srebot]

cherry-pick #2217 to release-5.0
You can switch your code base to this Pull Request by using git-extras:

# In tics repo:
git pr https://github.com/pingcap/tics/pull/2580

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tics.git pr/2580:release-5.0-df296ed35746

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What problem does this PR solve?

Related to #1901

Problem Summary:

Pushdown all mathematics functions to tiflash(except sqrt, ceil, floor and round because they've been already supported by #2090)

What is changed and how it works?

Proposal: xxx

What's Changed:

• FunctionsMath.h to impl log, ln, log2, log10, exp, pow, sign, degrees, radians
• FunctionsMath.cpp to register
• FunctionsStringMath.h to impl crc32 and conv
• FunctionsStringMath.cpp to register
• DAGUtils.cpp to modify scalar_func_map to update pushdown list
• math_func.test to test

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch:

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

Release note

• No release note

[windtalker]

close as it is not needed in 5.0.x