Add DATE TO DATE and TIMESTAMP TO DATE casting functions.

[mxwli]

Closes #3218

DATE TO DATE casting is called when casting nested datatypes, eg LISTS and STRUCTS, and so registering it is necessary. See the linked issue for an example.

TIMESTAMP to DATE casting uses Timestamp::getDate.

[codecov]

Codecov Report

Attention: Patch coverage is 96.42857% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 92.28%. Comparing base (d946982) to head (06f4fb8).
Report is 7 commits behind head on master.

❗ Current head 06f4fb8 differs from pull request most recent head 299f869. Consider uploading reports for the commit 299f869 to get more accurate results

Files	Patch %	Lines
src/function/vector_cast_functions.cpp	95.83%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3220      +/-   ##
==========================================
- Coverage   92.28%   92.28%   -0.01%     
==========================================
  Files        1161     1161              
  Lines       44150    43926     -224     
==========================================
- Hits        40744    40536     -208     
+ Misses       3406     3390      -16     

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[mxwli]

note: in copying the ValueVector in resolving nested types, an assert for resultVector.state.selVector.isUnfiltered is not made. This is in line with CastChildFunctionExecutor::executeSwitch, which is the function that would have run previously.