Make sure undefined tree-sitter thing doesn't raise an error

Make sure undefined tree-sitter thing doesn't raise an error

A previous change should've achived this, but that wasn't enough.
This one actually achieves the intended effect, namely,
treesit-node-match-p doesn't raise an error if IGNORE-MISSING is
non-nil, and traverse functions don't raise error by default.

* src/treesit.c (treesit_traverse_validate_predicate): Remove
ignore_missing parameter, return error symbol.
(Ftreesit_node_match_p)
(Ftreesit_search_subtree)
(Ftreesit_search_forward)
(Ftreesit_induce_sparse_tree): Check returned error symbol.
(syms_of_treesit): New symbol.