Rollup merge of #99903 - gimbles:pub, r=davidtwco

Add diagnostic when using public instead of pub

Forwarding from https://github.com/rust-lang/rust/pull/99706

I accidentally broke something(??) in git and the commits in that PR are absolutely not what I did in that branch

Anyways, this is the PR for this now. Adding tests again in a minute.

cc `@davidtwco`

src/test/ui/parser/public-instead-of-pub.fixed

@@ -0,0 +1,8 @@
+// Checks what happens when `public` is used instead of the correct, `pub`
+// edition:2018
+// run-rustfix
+pub struct X;
+//~^ ERROR expected one of `!` or `::`, found keyword `struct`
+//~^^ HELP write `pub` instead of `public` to make the item public
+
+fn main() {}

src/test/ui/parser/public-instead-of-pub.rs

@@ -0,0 +1,8 @@
+// Checks what happens when `public` is used instead of the correct, `pub`
+// edition:2018
+// run-rustfix
+public struct X;
+//~^ ERROR expected one of `!` or `::`, found keyword `struct`
+//~^^ HELP write `pub` instead of `public` to make the item public
+
+fn main() {}

src/test/ui/parser/public-instead-of-pub.stderr

@@ -0,0 +1,13 @@
+error: expected one of `!` or `::`, found keyword `struct`
+  --> $DIR/public-instead-of-pub.rs:4:8
+   |
+LL | public struct X;
+   |        ^^^^^^ expected one of `!` or `::`
+   |
+help: write `pub` instead of `public` to make the item public
+   |
+LL | pub struct X;
+   | ~~~
+
+error: aborting due to previous error
+