Add typed literal casting, rework typed literal casting

[andyfengHKU]

This PR contains the following changes

• Add casting function to RDF_VARIANT, RDF_VARIANT can be casted to any data type. On casting failure, instead of throwing runtime exception, we set casting result to NULL.
• Rework casting framework. We now only expose one bindCastFunction interface which returns a casting function for a given pair of src and dst type.

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (79999ec) 90.40% compared to head (b68bc6c) 90.46%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2347      +/-   ##
==========================================
+ Coverage   90.40%   90.46%   +0.05%     
==========================================
  Files        1013     1013              
  Lines       33050    33181     +131     
==========================================
+ Hits        29880    30016     +136     
+ Misses       3170     3165       -5     

Files	Coverage Δ
src/binder/expression_binder.cpp	95.29% <100.00%> (ø)
src/common/types/types.cpp	0.00% <ø> (ø)
src/function/built_in_functions.cpp	100.00% <100.00%> (ø)
src/function/vector_cast_functions.cpp	97.36% <100.00%> (+22.36%)	⬆️
src/include/common/types/blob.h	100.00% <100.00%> (ø)
src/include/function/scalar_function.h	100.00% <100.00%> (ø)
src/include/function/unary_function_executor.h	90.24% <100.00%> (+2.43%)	⬆️
src/processor/operator/persistent/copy_to_csv.cpp	96.87% <100.00%> (+0.03%)	⬆️
src/function/cast/cast_rdf_variant.cpp	96.93% <96.93%> (ø)

... and 4 files with indirect coverage changes

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