Fix array type handling in IsTextLikeType for USING clause generation

[Copilot]

The IsTextLikeType function didn't strip array suffixes before checking base types, causing incorrect USING clause logic for array type conversions (e.g., text[] → custom_enum[]).

Changes

• ir/normalize.go: Add strings.TrimSuffix(t, "[]") to IsTextLikeType, matching the pattern in IsBuiltInType
• testdata/diff/create_table/alter_column_types: Add text[] → enum[] conversion test case to existing test

Example

-- Before: Missing USING clause for array conversions
ALTER TABLE products ALTER COLUMN tags TYPE tag_type[];

-- After: Correctly generates USING clause
ALTER TABLE products ALTER COLUMN tags TYPE tag_type[] USING tags::tag_type[];

The fix ensures array types like text[], varchar[], and char[] are recognized as text-like, triggering USING clause generation for conversions involving custom types.

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[tianzhou]

@copilot you should not create new text cases. Instead you should add the text[] to the existing testdata/diff/create_table/alter_column_types

[Copilot]

@copilot you should not create new text cases. Instead you should add the text[] to the existing testdata/diff/create_table/alter_column_types

Done in ab0b6bb. Removed the separate test directories and added the text[] → action_type[] conversion to the existing alter_column_types test.