types2: no type reported for argument to unsafe.OffsetOf

Test case provided by @danscales :
```Go
package p

import "unsafe"

type Tstruct[T any] struct {
	f1 T
	f2 int
}

func (r *Tstruct[T]) offset() uintptr {
	return unsafe.Offsetof(r.f2)
}
```
types2.Info doesn't report a type for `r.f2`.