Add MAP_CONCAT internal function

[ykmr1224]

Description

• Add MAP_CONCAT internal function for dynamic fields implementation
  • It will be used to merge dynamic fields map among inputs (mainly join), where same key will be overwritten by later input.
• It is referring Spark library implementation
• Added integration test to verify its behavior and access to the function (manual RelNode generation to avoid exposing function in PPL syntax)

Related Issues

• [RFC] Dynamic Fields in PPL Calcite Implementation #4433
• (Calcite PPL) spath command dynamic columns support #4307

Check List

• New functionality includes testing.
• New functionality has been documented.
• New functionality has javadoc added.
• New functionality has a user manual doc added.
• New PPL command checklist all confirmed.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff or -s.
• Public documentation issue/PR created.

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[penghuo]

Not sure. Do we need map_concat or map_zip_with?

spark-sql (default)> SELECT map_zip_with(map(1, 'a', 2, 'b'), map(1, 'x', 2, 'y'), (k, v1, v2) -> array(v1, v2)) as res;
res
{1:["a","x"],2:["b","y"]}

[ykmr1224]

Not sure. Do we need map_concat or map_zip_with?

spark-sql (default)> SELECT map_zip_with(map(1, 'a', 2, 'b'), map(1, 'x', 2, 'y'), (k, v1, v2) -> array(v1, v2)) as res;
res
{1:["a","x"],2:["b","y"]}

That sounds more related to MAP_APPEND which I am planning to implement, and that will be used to merge dynamic fields when spath command is executed (because spath command needs to append instead of replace).
MAP_CONAT is different because it will simply overwrite value in case of key conflict. This is needed mainly for join operation where we don't merge values.