handle bracket stack better in recdescent parsing

handle bracket stack better in recdescent parsing

When recursing into the parser for recursive-descent parsing, put
a special entry on the bracket stack that generates a fake EOF if a
closing bracket belonging to an outer parser frame is seen.  This keeps
the bracket stack balanced across a parse_stmtseq() frame, fixing
[perl #78222].

If a recursive-descent parser frame ends by yyunlex()ing an opening
bracket, pop its entry off the bracket stack and stash it in the
forced-token queue, to be revived when the token is re-lexed.  This keeps
the bracket stack balanced across a parse_fullstmt() frame.