Fix ${!} and ${$} throwing syntax error in here-document

The inclusion of the special parameter expansions ${!} and ${$}
(including the braces) in a here-document caused a syntax error.
Bug reported by @Saikiran-m on Github.

src/cmd/ksh93/data/lexstates.c: sh_lexstate7[]:
- Change the state for ! (33) and $ (36) from S_ERR to 0. State
  table 7 is for skipping over ${...}, so this avoids the S_ERR
  state being invoked in sh_lex() (lex.c) for these characters
  while skipping ${...} in a here-doc.

src/cmd/ksh93/tests/heredoc.sh:
- Test evaluating the braces expansion form for all special
  parameters (@ * # ! $ - ? 0) in a here-document.

Fixes: https://github.com/ksh93/ksh/issues/127

src/cmd/ksh93/data/lexstates.c

@@ -274,7 +274,7 @@ static const char sh_lexstate7[256] =
 	S_ERR,	S_ERR,	S_ERR,	S_ERR,	S_ERR,	S_ERR,	S_ERR,	S_ERR,
 	S_ERR,	S_ERR,	S_ERR,	S_ERR,	S_ERR,	S_ERR,	S_ERR,	S_ERR,
 
-	S_ERR,	S_ERR,	S_ERR,	S_MOD2,	S_ERR,	S_MOD2,	S_ERR,	S_ERR,
+	S_ERR,	0,	S_ERR,	S_MOD2,	0,	S_MOD2,	S_ERR,	S_ERR,
 	S_ERR,	S_ERR,	S_MOD1,	S_MOD1,	S_ERR,	S_MOD1,	S_DOT,	S_MOD2,
 	0,	0,	0,	0,	0,	0,	0,	0,
 	0,	0,	S_MOD1,	S_ERR,	S_ERR,	S_MOD1,	S_ERR,	S_MOD1,

src/cmd/ksh93/tests/heredoc.sh

@@ -509,5 +509,15 @@ EOF' || err_exit 'placing a command substitution and here-doc on the same line c
 $SHELL -c '$(true << !)
 !' 2> /dev/null && err_exit "a here-doc that isn't completed before the closing ) in a command substitution doesn't cause an error"
 
+# ======
+# Check that ${p}, where p is a special parameter, does not cause a syntax error in a here-document.
+# Bug for ${!} and ${$} reported at: https://github.com/ksh93/ksh/issues/127
+for p in @ \* \# ! \$ - \? 0; do
+	err=$(eval ': <<EOF
+${'"$p"'}
+EOF
+' 2>&1) || err_exit "special parameter \${$p} throws syntax error in here-document (got \"$err\")"
+done
+
 # ======
 exit $((Errors<125?Errors:125))