Enable Optional Match as the First Clause

[andyfengHKU]

This PR enables the following pattern OPTIONAL MATCH ... RETURN .... This is a pre-request for MERGE

[codecov]

Codecov Report

Patch coverage: 95.29% and project coverage change: -0.01 ⚠️

Comparison is base (77c7829) 91.30% compared to head (67d8968) 91.29%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1849      +/-   ##
==========================================
- Coverage   91.30%   91.29%   -0.01%     
==========================================
  Files         792      792              
  Lines       28765    28778      +13     
==========================================
+ Hits        26264    26273       +9     
- Misses       2501     2505       +4     

Impacted Files	Coverage Δ
src/binder/bind/bind_query.cpp	100.00% <ø> (ø)
src/binder/binder.cpp	96.33% <ø> (-0.13%)	⬇️
src/include/binder/binder.h	100.00% <ø> (ø)
src/include/parser/query/single_query.h	100.00% <ø> (ø)
src/include/planner/join_order_enumerator.h	100.00% <ø> (ø)
src/include/planner/query_planner.h	100.00% <ø> (ø)
src/include/processor/mapper/plan_mapper.h	100.00% <ø> (ø)
...ude/processor/operator/hash_join/hash_join_probe.h	100.00% <ø> (ø)
src/optimizer/optimizer.cpp	100.00% <ø> (ø)
src/processor/mapper/map_union.cpp	100.00% <ø> (ø)
... and 22 more

... and 6 files with indirect coverage changes

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