More explicit diagnostic when using a `vec![]` in a pattern
```
error: unexpected `(` after qualified path
--> $DIR/vec-macro-in-pattern.rs:3:14
|
LL | Some(vec![x]) => (),
| ^^^^^^^
| |
| unexpected `(` after qualified path
| in this macro invocation
| use a slice pattern here instead
|
= help: for more information, see https://doc.rust-lang.org/edition-guide/rust-2018/slice-patterns.html
= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
```
Fix #61933.