Add spacing information to delimiters.

This is an extension of the previous commit. It means the output of
something like this:
```
stringify!(let a: Vec<u32> = vec![];)
```
goes from this:
```
let a: Vec<u32> = vec![] ;
```
With this PR, it now produces this string:
```
let a: Vec<u32> = vec![];
```

compiler/rustc_expand/src/config.rs

@@ -6,8 +6,7 @@ use crate::errors::{
 };
 use rustc_ast::ptr::P;
 use rustc_ast::token::{Delimiter, Token, TokenKind};
-use rustc_ast::tokenstream::{AttrTokenStream, AttrTokenTree};
-use rustc_ast::tokenstream::{DelimSpan, Spacing};
+use rustc_ast::tokenstream::{AttrTokenStream, AttrTokenTree, DelimSpacing, DelimSpan, Spacing};
 use rustc_ast::tokenstream::{LazyAttrTokenStream, TokenTree};
 use rustc_ast::NodeId;
 use rustc_ast::{self as ast, AttrStyle, Attribute, HasAttrs, HasTokens, MetaItem};
@@ -242,7 +241,7 @@ impl<'a> StripUnconfigured<'a> {
             stream.0.iter().all(|tree| match tree {
                 AttrTokenTree::Attributes(_) => false,
                 AttrTokenTree::Token(..) => true,
-                AttrTokenTree::Delimited(_, _, inner) => can_skip(inner),
+                AttrTokenTree::Delimited(.., inner) => can_skip(inner),
             })
         }
 
@@ -266,9 +265,9 @@ impl<'a> StripUnconfigured<'a> {
                         None.into_iter()
                     }
                 }
-                AttrTokenTree::Delimited(sp, delim, mut inner) => {
+                AttrTokenTree::Delimited(sp, spacing, delim, mut inner) => {
                     inner = self.configure_tokens(&inner);
-                    Some(AttrTokenTree::Delimited(sp, delim, inner)).into_iter()
+                    Some(AttrTokenTree::Delimited(sp, spacing, delim, inner)).into_iter()
                 }
                 AttrTokenTree::Token(ref token, _)
                     if let TokenKind::Interpolated(nt) = &token.kind =>
@@ -376,6 +375,7 @@ impl<'a> StripUnconfigured<'a> {
         // in `#[attr]`, so just use the span of the `#` token.
         let bracket_group = AttrTokenTree::Delimited(
             DelimSpan::from_single(pound_span),
+            DelimSpacing::new(Spacing::JointHidden, Spacing::Alone),
             Delimiter::Bracket,
             item.tokens
                 .as_ref()