[ADT] Fix ArrayRef<T>::slice (llvm#113048)

Current implementation of `slice(N)` is buggy, since
`slice(N, size() - N)` will never fail the assertion
`assert(N+M <= size() && "Invalid specifier")` above, even
`N > size()`.

Author: FLZ101

llvm/include/llvm/ADT/ArrayRef.h

@@ -198,7 +198,7 @@ namespace llvm {
     }
 
     /// slice(n) - Chop off the first N elements of the array.
-    ArrayRef<T> slice(size_t N) const { return slice(N, size() - N); }
+    ArrayRef<T> slice(size_t N) const { return drop_front(N); }
 
     /// Drop the first \p N elements of the array.
     ArrayRef<T> drop_front(size_t N = 1) const {