Remove LOAD/STORE/RETURN boilerplate in declarative builders.

This CL introduces a ValueArrayHandle helper to manage the implicit conversion
of ArrayRef<ValueHandle> -> ArrayRef<Value*> by converting first to ValueArrayHandle.
Without this, boilerplate operations that take ArrayRef<Value*> cannot be removed easily.

This all seems to boil down to decoupling Value from Type.
Alternative solutions exist (e.g. MLIR using Value by value everywhere) but they would be very intrusive. This seems to be the lowest impedance change.

Intrinsics are also lowercased by popular demand.

PiperOrigin-RevId: 238974125