Implemented value tuple literal in SQL

[egormanga]

Description of Changes

There's been no way to use product types like this:

struct Position<T: geo::CoordNum = Coord> {
	lat: T,
	lon: T,
}

#[table(name=point)]
struct Point {
	pos: Position,
}

because SQL queries containing tuples:

SELECT * FROM point WHERE pos = (0, 0);

would fail with:
Error: Unsupported expression: (0, 0)

This PR implements tuple support for = and != operators (subject to further expansion).

API and ABI breaking changes

None.

Expected complexity level and risk

2.

Testing

• Manual testing using custom struct columns.
• Needs unit tests. I leave this open for contributions or as an exercise to the employees.

[egormanga]

Possibly related to #2670?