Implement union functions

[acquamarin]

This PR is the first set of PRs to implement UNION datatype in kuzu.
KUZU stores UNION as a struct where the first field is the tag field indicating the selected member. Similar to C++ union, Only one member can be selected at a time.
It introduces 3 basic union functions:

1. UNION_VALUE: creates a single member UNION containing the argument value. The tag of the value will be the bound variable name.
2. UNION_TAG: returns the selected member name.
3. UNION_EXTRACT: extracts a union field. If the field is not selected, NULL will be returned.

[codecov]

Codecov Report

Patch coverage: 90.86% and project coverage change: -0.03 ⚠️

Comparison is base (904c585) 91.44% compared to head (d4dfe64) 91.42%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1675      +/-   ##
==========================================
- Coverage   91.44%   91.42%   -0.03%     
==========================================
  Files         730      732       +2     
  Lines       26475    26575     +100     
==========================================
+ Hits        24211    24295      +84     
- Misses       2264     2280      +16     

Impacted Files	Coverage Δ
src/common/types/types.cpp	88.76% <0.00%> (-2.51%)	⬇️
src/include/common/types/value.h	100.00% <ø> (ø)
src/include/common/vector/auxiliary_buffer.h	90.90% <ø> (ø)
src/include/function/binary_operation_executor.h	75.42% <ø> (ø)
src/include/function/built_in_vector_operations.h	100.00% <ø> (ø)
.../include/function/schema/vector_label_operations.h	100.00% <ø> (ø)
...include/function/struct/vector_struct_operations.h	100.00% <ø> (ø)
src/include/function/ternary_operation_executor.h	31.72% <ø> (ø)
src/include/function/unary_operation_executor.h	86.48% <ø> (ø)
src/include/parser/transformer.h	100.00% <ø> (ø)
... and 15 more

... and 1 file with indirect coverage changes

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