Consider unfulfilled obligations in binop errors

When encountering a binop where the types would have been accepted, if
all the predicates had been fulfilled, include information about the
predicates and suggest appropriate `#[derive]`s if possible.

Point at trait(s) that needs to be `impl`emented.

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -521,7 +521,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                                     "this error might have been caused by changes to \
                                     Rust's type-inference algorithm (see issue #48950 \
                                     <https://github.com/rust-lang/rust/issues/48950> \
-                                    for more information).",
+                                    for more information)",
                                 );
                                 err.help("did you intend to use the type `()` here instead?");
                             }