Incorrect error message and error location for invalid escape sequences

[serpent7776]

Incorrect error message and error location for invalid escape sequences:

{
	"": "foobar\?"
}

Current message:

Error: Parse error on line 2:
{	"": "foobar\?"}
------^
Expecting 'STRING', 'NUMBER', 'NULL', 'TRUE', 'FALSE', '{', '[', got 'undefined'

Expected error message:

Invalid escape sequence \?

Error location should point directly at \?. Current location is especially confusing for very long strings.