Add ptr::Pointee trait (for all types) and ptr::metadata function

RFC: https://github.com/rust-lang/rfcs/pull/2580

compiler/rustc_span/src/symbol.rs

@@ -476,6 +476,7 @@ symbols! {
         dropck_eyepatch,
         dropck_parametricity,
         dylib,
+        dyn_metadata,
         dyn_trait,
         edition_macro_pats,
         eh_catch_typeinfo,
@@ -710,6 +711,7 @@ symbols! {
         memory,
         message,
         meta,
+        metadata_type,
         min_align_of,
         min_align_of_val,
         min_const_fn,
@@ -832,6 +834,7 @@ symbols! {
         plugin,
         plugin_registrar,
         plugins,
+        pointee_trait,
         pointer,
         pointer_trait,
         pointer_trait_fmt,