Auto merge of #25688 - nham:E0055_E0192, r=alexcrichton

- Adds explanations for E0055, E0089, E0192, E0261-E0263, E0318
 - Improves explanations for E0250, E0368, E0372.
 - Converts 15 diagnostics to have error codes (E0380-E0394). Adds an explanation for E0380.
 - The E0087-E0090 messages currently look like "expected {} parameter(s) found {} parameter(s)". This changes them to either use "parameter" or "parameters", based on the number.

This is, in part, more progress towards #24407

src/test/compile-fail/syntaxt-default-trait-impls.rs

@@ -13,6 +13,6 @@
 trait MyDefaultImpl {}
 
 impl<T> MyDefaultImpl for .. {}
-//~^ ERROR default trait implementations are not allowed to have genercis
+//~^ ERROR default trait implementations are not allowed to have generics
 
 fn main() {}

src/test/compile-fail/ufcs-qpath-missing-params.rs

@@ -12,5 +12,5 @@ use std::borrow::IntoCow;
 
 fn main() {
     <String as IntoCow>::into_cow("foo".to_string());
-    //~^ ERROR too few type parameters provided: expected 1 parameter(s)
+    //~^ ERROR too few type parameters provided: expected 1 parameter
 }