AK: Forbid from_utf8 and from_deprecated_{...} with unintended types

Calling `from_utf8` with a DeprecatedString will hide the fact that we
have a DeprecatedString, while using `from_deprecated_string` with a
StringView will silently and needlessly allocate a DeprecatedString,
so let's forbid that.

Userland/Libraries/LibCore/System.cpp

@@ -1047,7 +1047,7 @@ ErrorOr<String> mkdtemp(Span<char> pattern)
         return Error::from_errno(errno);
     }
 
-    return String::from_utf8({ path, strlen(path) });
+    return String::from_utf8(StringView { path, strlen(path) });
 }
 
 ErrorOr<void> rename(StringView old_path, StringView new_path)