Parsing of "?[" as two tokens (makes ssr compile).
Parsing of "?[" as two tokens (makes ssr compile).

The problem is that "?[" makes the lexer glue "?" and "[" into
a single token but in ssr "?" (iteration) and "[" (rewrite pattern
delimiter) are often close, but they are parsed by very hard to
refactor grammar entries.

To consider:
- check the adjacency of the two symbols looking at the loc to
  parse exactly the same sentences as before this patch
- change syntax completely, e.g. "(_ as id)"

gares/coq,Matafou/coq,ppedrot/coq,amintimany/coq,letouzey/coq-wip,coq/coq,maximedenes/coq,william-lawvere/coq,ale-f/coq,barras/coq,barras/coq,SkySkimmer/coq,coq/coq,Matafou/coq,JasonGross/coq,ppedrot/coq,william-lawvere/coq,william-lawvere/coq,TOSPIO/coq,herbelin/github-coq,asr/coq,gmalecha/coq,TOSPIO/coq,gmalecha/coq,Lionel-Rieg/coq,SkySkimmer/coq,maximedenes/coq,Matafou/coq,Ptival/coq,Ptival/coq,letouzey/coq-wip,pirapira/coq2rust,TheTypoMaster/coq,ale-f/coq,silene/coq,maximedenes/coq,ejgallego/coq,letouzey/coq-wip,TheTypoMaster/coq,JasonGross/coq,TOSPIO/coq,gmalecha/coq,Lionel-Rieg/coq,pirapira/coq2rust,silene/coq,8l/coq,SkySkimmer/coq,asr/coq,jpdeplaix/coq,maximedenes/coq,gares/coq,mlasson/coq,amintimany/coq,shindere/coq,ppedrot/coq,pirapira/coq2rust,shindere/coq,Zimmi48/coq,Zimmi48/coq,ejgallego/coq,shindere/coq,jpdeplaix/coq,JasonGross/coq,herbelin/github-coq,ppedrot/coq,TheTypoMaster/coq,asr/coq,Zimmi48/coq,ejgallego/coq,8l/coq,aspiwack/coq,jpdeplaix/coq,mattam82/coq,gares/coq,mlasson/coq,ppedrot/coq,Zimmi48/coq,silene/coq,aspiwack/coq,gares/coq,letouzey/coq-wip,8l/coq,coq/coq,SkySkimmer/coq,mlasson/coq,amintimany/coq,herbelin/github-coq,gares/coq,Ptival/coq,maximedenes/coq,letouzey/coq-wip,ejgallego/coq,barras/coq,Lionel-Rieg/coq,ale-f/coq,aspiwack/coq,mattam82/coq,JasonGross/coq,mattam82/coq,coq/coq