Disallow traversal patterns outside of the appropriate clauses

[jeffreylovitz]

Cypher allows traversal patterns to appear in a number of unexpected places, such as:

MATCH (a) RETURN (a)-[]->()
MATCH (a) RETURN a ORDER BY (a)-[]->()
MATCH (a {prop: ()-[]->()}) RETURN a

These constructions don't seem useful to me, and they often cause crashes because QueryGraph construction collects all paths in an AST:
https://github.com/RedisGraph/RedisGraph/blob/master/src/graph/query_graph.c#L301

This PR disallows all such constructions by introducing a whitelist of the AST nodes that can validly have traversals as their children.

Resolves #1428

[swilly22]

Fuzzer starting to show dividends! this is great.

[swilly22]

Nice!
Consider

q0 = """MATCH (a {prop: ()-[]->()}) RETURN a"""
q1 = """MATCH (a) RETURN a ORDER BY (a)-[]->()"""
q2 = """MATCH (a) RETURN (a)-[]->()"""
queries = [q0, q1, q2]
for q in queries:
    try:            
            redis_graph.query(q)
            assert(False)
        except redis.exceptions.ResponseError as e:
            assert("Encountered path traversal" in e.message)
            pass

[swilly22]

Please add a comment giving some information about what this function do

[swilly22]

Remove extra new line

[swilly22]

I think we can improve a bit by relocating this block:

for(uint i = 0; i < nchildren; i ++) {
    const cypher_astnode_t *child = cypher_astnode_get_child(root, i);
    if(cypher_astnode_type(child) == CYPHER_AST_PATTERN_PATH) {
        const cypher_astnode_type_t root_type = cypher_astnode_type(root);
        if(root_type == CYPHER_AST_PATTERN ||
			root_type == CYPHER_AST_MATCH ||
			root_type == CYPHER_AST_MERGE ||
			root_type == CYPHER_AST_WITH ||
			root_type == CYPHER_AST_NAMED_PATH ||
			root_type == CYPHER_AST_UNARY_OPERATOR ||
			root_type == CYPHER_AST_BINARY_OPERATOR) {
		valid_caller = true;
	}
        if(!valid_caller) {
            QueryCtx_SetError("Encountered path traversal in unsupported location '%s'", cypher_astnode_typestr(cypher_astnode_type(child)));
            return AST_INVALID;
}...

Also might be faster to match invalid_caller if the list of clauses is shorter.