Auto merge of #36969 - nnethercote:rename-Parser-fields, r=eddyb

Clarify the positions of the lexer and parser

The lexer and parser use unclear names to indicate their positions in the
source code. I propose the following renamings.

Lexer:
```
pos      -> next_pos      # it's actually the next pos!
last_pos -> pos           # it's actually the current pos!
curr     -> ch            # the current char
curr_is  -> ch_is         # tests the current char
col (unchanged)           # the current column
```
parser
```
- last_span       -> prev_span          # the previous token's span
- last_token_kind -> prev_token_kind    # the previous token's kind
- LastTokenKind   -> PrevTokenKind      # ditto (but the type)
- token (unchanged)                     # the current token
- span (unchanged)                      # the current span
```

Things to note:
- This proposal removes all uses of "last", which is an unclear word because it
  could mean (a) previous, (b) final, or (c) most recent, i.e. current.
- The "current" things (ch, col, token, span) consistently lack a prefix. The
  "previous" and "next" things consistently have a prefix.

0 files changed, 0 insertions, 0 deletions