Changed lint to check for std::fmt::Pointer and transmute

The lint checks arguments in calls to `transmute` or functions that have
`Pointer` as a trait bound and displays a warning if the argument is a function
reference. Also checks for `std::fmt::Pointer::fmt` to handle formatting macros
although it doesn't depend on the exact expansion of the macro or formatting
internals. `std::fmt::Pointer` and `std::fmt::Pointer::fmt` were also added as
diagnostic items and symbols.

Author: ayrtonm

core/src/fmt/mod.rs

@@ -920,9 +920,11 @@ pub trait UpperHex {
 /// assert_eq!(&l_ptr[..2], "0x");
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_diagnostic_item = "pointer_trait"]
 pub trait Pointer {
     /// Formats the value using the given formatter.
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_diagnostic_item = "pointer_trait_fmt"]
     fn fmt(&self, f: &mut Formatter<'_>) -> Result;
 }