case with /eggex/ can be confused with glob /foo/bar/*

[andychu]

https://oilshell.zulipchat.com/#narrow/channel/264891-oil-help/topic/glob.20starting.20with.20slash.20in.20case

[andychu]

crash in Python version

$ bin/ysh -c 'case ("/foo/bar/") { \/foo/* { echo hi } }'
Traceback (most recent call last):
  File "/home/andy/git/oils-for-unix/oils/bin/oils_for_unix.py", line 202, in <module>
    sys.exit(main(sys.argv))

[andychu]

Inconsistency in whether it is flagged, depending on the line

$ cat g.ysh
case ('/foo/bar') {
  \/foo/* { echo hi } 
}

$ cat g2.ysh
case ('/foo/bar') { \/foo/* { echo hi } }

$ ysh g.ysh

$ ysh g2.ysh
  case ('/foo/bar') { \/foo/* { echo hi } }
                      ^~
g2.ysh:1: Invalid char escape in unquoted word (OILS-ERR-13)

Expected: g.ysh should also give an error

[andychu]

Some how in the first case we are missing \ in the SQ node

$ ysh -n g.ysh
(command.Case case_kw:<KW_Case case> to_match:(case_arg.YshExpr e:(SQ /foo/bar)) arms_start:<Lit_LBrace "{"> arms:[] arms_end:<Lit_RBrace "}">)
andy@hoover:~/git/oils-for-unix/oils$ ysh g.ysh
andy@hoover:~/git/oils-for-unix/oils$ cat g.ysh
case ('/foo/bar') {
  \/foo/* { echo hi } 
}