Add `ErrorGuaranteed` to `Recovered::Yes` and use it more.

The starting point for this was identical comments on two different
fields, in `ast::VariantData::Struct` and `hir::VariantData::Struct`:
```
    // FIXME: investigate making this a `Option<ErrorGuaranteed>`
    recovered: bool
```
I tried that, and then found that I needed to add an `ErrorGuaranteed`
to `Recovered::Yes`. Then I ended up using `Recovered` instead of
`Option<ErrorGuaranteed>` for these two places and elsewhere, which
required moving `ErrorGuaranteed` from `rustc_parse` to `rustc_ast`.

This makes things more consistent, because `Recovered` is used in more
places, and there are fewer uses of `bool` and
`Option<ErrorGuaranteed>`. And safer, because it's difficult/impossible
to set `recovered` to `Recovered::Yes` without having emitted an error.

1 files changed, 4 insertions, 1 deletions

diff --git a/tests/ui-fulldeps/pprust-expr-roundtrip.rs b/tests/ui-fulldeps/pprust-expr-roundtrip.rs
index 475a69f4ad0..2b1fec94387 100644
--- a/tests/ui-fulldeps/pprust-expr-roundtrip.rs
+++ b/tests/ui-fulldeps/pprust-expr-roundtrip.rs
@@ -180,7 +180,10 @@ fn iter_exprs(depth: usize, f: &mut dyn FnMut(P<Expr>)) {
             18 => {
                 let pat =
                     P(Pat { id: DUMMY_NODE_ID, kind: PatKind::Wild, span: DUMMY_SP, tokens: None });
-                iter_exprs(depth - 1, &mut |e| g(ExprKind::Let(pat.clone(), e, DUMMY_SP, None)))
+                iter_exprs(
+                    depth - 1,
+                    &mut |e| g(ExprKind::Let(pat.clone(), e, DUMMY_SP, Recovered::No))
+                )
             }
             _ => panic!("bad counter value in iter_exprs"),
         }