Add MAP_CONCAT, MAP_FROM_ENTRIES for Spark dialect

map_concat

map_concat(map, ...) - Returns the union of all the given maps

Examples:

> SELECT map_concat(map(1, 'a', 2, 'b'), map(3, 'c'));
 {1:"a",2:"b",3:"c"} 

map_from_entries

map_from_entries(arrayOfEntries) - Returns a map created from the given array of entries.

Examples:

> SELECT map_from_entries(array(struct(1, 'a'), struct(2, 'b')));
 {1:"a",2:"b"}