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_borrowck/src/diagnostics/mod.rs

@@ -570,7 +570,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         // If we didn't find an overloaded deref or index, then assume it's a
         // built in deref and check the type of the base.
         let base_ty = deref_base.ty(self.body, tcx).ty;
-        if base_ty.is_unsafe_ptr() {
+        if base_ty.is_raw_ptr() {
             BorrowedContentSource::DerefRawPointer
         } else if base_ty.is_mutable_ptr() {
             BorrowedContentSource::DerefMutableRef