Speed up Parser::expected_token_types.

The parser pushes a `TokenType` to `Parser::expected_token_types` on
every call to the various `check`/`eat` methods, and clears it on every
call to `bump`. Some of those `TokenType` values are full tokens that
require cloning and dropping. This is a *lot* of work for something
that is only used in error messages and it accounts for a significant
fraction of parsing execution time.

This commit overhauls `TokenType` so that `Parser::expected_token_types`
can be implemented as a bitset. This requires changing `TokenType` to a
C-style parameterless enum, and adding `TokenTypeSet` which uses a
`u128` for the bits. (The new `TokenType` has 105 variants.)

The new types `ExpTokenPair` and `ExpKeywordPair` are now arguments to
the `check`/`eat` methods. This is for maximum speed. The elements in
the pairs are always statically known; e.g. a
`token::BinOp(token::Star)` is always paired with a `TokenType::Star`.
So we now compute `TokenType`s in advance and pass them in to
`check`/`eat` rather than the current approach of constructing them on
insertion into `expected_token_types`.

Values of these pair types can be produced by the new `exp!` macro,
which is used at every `check`/`eat` call site. The macro is for
convenience, allowing any pair to be generated from a single identifier.

The ident/keyword filtering in `expected_one_of_not_found` is no longer
necessary. It was there to account for some sloppiness in
`TokenKind`/`TokenType` comparisons.

The existing `TokenType` is moved to a new file `token_type.rs`, and all
its new infrastructure is added to that file. There is more boilerplate
code than I would like, but I can't see how to make it shorter.

compiler/rustc_builtin_macros/src/util.rs

@@ -7,7 +7,7 @@ use rustc_expand::expand::AstFragment;
 use rustc_feature::AttributeTemplate;
 use rustc_lint_defs::BuiltinLintDiag;
 use rustc_lint_defs::builtin::DUPLICATE_MACRO_ATTRIBUTES;
-use rustc_parse::{parser, validate_attr};
+use rustc_parse::{exp, parser, validate_attr};
 use rustc_session::errors::report_lit_error;
 use rustc_span::{BytePos, Span, Symbol};
 
@@ -204,7 +204,7 @@ pub(crate) fn get_single_expr_from_tts(
         Ok(ret) => ret,
         Err(guar) => return ExpandResult::Ready(Err(guar)),
     };
-    let _ = p.eat(&token::Comma);
+    let _ = p.eat(exp!(Comma));
 
     if p.token != token::Eof {
         cx.dcx().emit_err(errors::OnlyOneArgument { span, name });
@@ -237,7 +237,7 @@ pub(crate) fn get_exprs_from_tts(
         let expr = cx.expander().fully_expand_fragment(AstFragment::Expr(expr)).make_expr();
 
         es.push(expr);
-        if p.eat(&token::Comma) {
+        if p.eat(exp!(Comma)) {
             continue;
         }
         if p.token != token::Eof {