Length() function implementation

[zenmiao7]

I hereby agree to the terms of the CLA available at: https://databend.rs/policies/cla/

Summary

Implement Length() function

Changelog

• New Feature

Related Issues

#3049

Test Plan

Unit Tests

Stateless Tests

[databend-bot]

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[codecov-commenter]

Codecov Report

Merging #3448 (2a35c41) into main (1f29cfc) will increase coverage by 0%.
The diff coverage is 14%.

@@          Coverage Diff          @@
##            main   #3448   +/-   ##
=====================================
  Coverage     61%     61%           
=====================================
  Files        610     611    +1     
  Lines      34185   34192    +7     
=====================================
+ Hits       20992   21003   +11     
+ Misses     13193   13189    -4     

Impacted Files	Coverage Δ
common/functions/src/scalars/strings/length.rs	0% <0%> (ø)
common/functions/src/scalars/strings/string.rs	97% <100%> (+<1%)	⬆️
metasrv/src/store/meta_raft_store.rs	80% <0%> (+2%)	⬆️
common/management/src/cluster/cluster_mgr.rs	81% <0%> (+2%)	⬆️

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[BohuTANG]

Stateless test failed:

[ FAIL ] - result differs with:
--- /home/runner/work/databend/databend/tests/suites/0_stateless/02_0040_function_strings_length.result	2021-12-13 23:12:56.176552939 +0000
+++ /home/runner/work/databend/databend/tests/suites/0_stateless/02_0040_function_strings_length.stdout	2021-12-13 23:19:15.927736136 +0000
@@ -1,5 +1,5 @@
-5
+4
 18
 28
-NULL
 6
+NULL

[BohuTANG]

/lgtm

[BohuTANG]

Unit Tests / Tests (macos-11) test failed is not related to this PR, merged.
Thank you @Blacksmith96 !