Resolve shift/reduce conflict of 'def' vs '|'

This was an important conflict. In the following expression:

    def a: 0; . | a

Bison needs to decide between these two equally valid
parses:

    (def a: 0; .) | a
    def a: 0; (. | a)

For jq we want the second one, because the first results in
"a/0 is not defined". In the current parser the first parse
is a reduce and the second parse is a shift. Since Bison
prefers to shift in shift/reduce conflicts, we accidentally
got the correct behavior.

This commit adds a precedence level FUNCDEF which is lower
precedence than '|', meaning we explicitly choose the
correct parse.

Of course many unit tests already cover this case, but I
added one specifically for it.

parser.y

@@ -91,8 +91,9 @@ struct lexer_param;
 %token QQSTRING_END
 
 /* see Exp '?' rule */
-%expect 34
+%expect 9
 
+%precedence FUNCDEF
 %right '|'
 %left ','
 %right "//"
@@ -306,7 +307,7 @@ FuncDef FuncDefs {
 }
 
 Exp:
-FuncDef Exp %prec ';' {
+FuncDef Exp %prec FUNCDEF {
   $$ = block_bind_referenced($1, $2, OP_IS_CALL_PSEUDO);
 } |