Rename rustc_middle::Ty::is_unsafe_ptr to is_raw_ptr

The wording unsafe pointer is less common and not mentioned in a lot of
places, instead this is usually called a "raw pointer". For the sake of
uniformity, we rename this method.
This came up during the review of
https://github.com/rust-lang/rust/pull/134424.

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -554,7 +554,7 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                             _ => self.requires_unsafe(expr.span, UseOfExternStatic),
                         }
                     }
-                } else if self.thir[arg].ty.is_unsafe_ptr() {
+                } else if self.thir[arg].ty.is_raw_ptr() {
                     self.requires_unsafe(expr.span, DerefOfRawPointer);
                 }
             }