[Refactoring] isAggregate
[stash] isUvalue
Revert "[stash] isUvalue"

This reverts commit cfefee334c41a0b56b56a62fad328baf4efb2f96.
[Refactoring] bool Expression::rvalue
[Refactoring] bool Expression::isBool(bool result)
[Refactoring] bool Type::isZeroInit(Loc)