Update BARE_TRAIT_OBJECT and ELLIPSIS_INCLUSIVE_RANGE_PATTERNS to errors in Rust 2021

compiler/rustc_error_codes/src/error_codes/E0782.md

@@ -0,0 +1,17 @@
+Trait objects must include the `dyn` keyword.
+
+Trait objects are a way to call methods on types that are not known until
+runtime but conform to some trait.
+
+In the following code the trait object should be formed with
+`Box<dyn Foo>`, but `dyn` is left off.
+
+```compile_fail,E0782
+trait Foo {}
+fn test(arg: Box<Foo>) {}
+```
+
+This makes it harder to see that `arg` is a trait object and not a
+simply a heap allocated type called `Foo`.
+
+This used to be allowed before edition 2021, but is now an error.

compiler/rustc_error_codes/src/error_codes/E0783.md

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+The range pattern `...` is no longer allowed.
+
+Older Rust code using previous editions allowed `...` to stand for exclusive
+ranges which are now signified using `..=`.
+
+The following code use to compile, but now it now longer does.
+
+```compile_fail,E0783
+fn main() {
+    let n = 2u8;
+    match n {
+        ...9 => println!("Got a number less than 10),
+        _ => println!("Got a number 10 or more")
+    }
+}
+```
+
+To make this code compile replace the `...` with `..=`.