fix(parser): support CAST to an array type for MySQL multi-valued indexes

[minleejae]

Refs #2490

Description

Fixes the last open group of #2490, group 6, multi-valued (functional) indexes:

CREATE INDEX i20 ON t ((CAST(data->'$.zips' AS UNSIGNED ARRAY)));
ALTER TABLE t ADD INDEX i31 ((CAST(data->'$.zips' AS UNSIGNED ARRAY)));

Both failed at the ARRAY keyword inside the cast target type, because that keyword was not reachable from the type of a CAST.

Approach

ARRAY is accepted as a further word of the cast target type, exactly the way INT UNSIGNED is already assembled by DataType(). The type therefore reads UNSIGNED ARRAY, so:

• no change to the public ColDataType model is needed, and
• both output paths, CastExpression#toString() and ExpressionDeParser, render it through the same ColDataType#toString(), so the statement round trips.

It is added to the CastExpression() production only, which is where MySQL permits it. The ARRAY<type> constructor form and the [] array suffix are untouched, and no other statement gains a trailing ARRAY.

If you would rather have this exposed as an explicit flag on ColDataType for programmatic access, say the word and I will change it.

Testing

• ./gradlew check passes: checkstyle, PMD, spotless, spotbugs, JaCoCo.
• 4927 tests, 0 failures, 0 errors.
• JavaCC reports 0 errors and 13 warnings, unchanged from master, verified by regenerating the parser on both states.
• Three new tests: the CREATE INDEX form, the ALTER TABLE form, and the cast itself, including CAST(x AS CHAR(10) ARRAY) to cover a type that carries a precision, plus an assertion that the parsed type is UNSIGNED ARRAY.
• Verified that CAST(x AS UNSIGNED) and ARRAY<INT>[1, 2] still parse unchanged.

All statements were verified against MySQL 8.4.11 while writing #2490.

PR Checklist

• I have read the contribution guidelines and the governance document on PR expectations.

[manticore-projects]

CREATE INDEX i20 ON t ((CAST(data->'$.zips' AS UNSIGNED ARRAY)));
ALTER TABLE t ADD INDEX i31 ((CAST(data->'$.zips' AS UNSIGNED ARRAY)));

They should have killed this when it was little still.
But since it seems to be useful to someone, so be it.