Make Parser::num_bump_calls 0-indexed.

Currently in `collect_tokens_trailing_token`, `start_pos` and `end_pos`
are 1-indexed by `replace_ranges` is 0-indexed, which is really
confusing. Making them both 0-indexed makes debugging much easier.

Author: nnethercote

compiler/rustc_parse/src/parser/mod.rs

@@ -435,6 +435,11 @@ impl<'a> Parser<'a> {
         // Make parser point to the first token.
         parser.bump();
 
+        // Change this from 1 back to 0 after the bump. This eases debugging of
+        // `Parser::collect_tokens_trailing_token` nicer because it makes the
+        // token positions 0-indexed which is nicer than 1-indexed.
+        parser.num_bump_calls = 0;
+
         parser
     }