Property names containing backslashes cannot be expressed in the syntax #203

Description

In jsonpath syntax (e.g. $["a\\b"]), there appears to be no way to express a property name that itself contains a backslash. Bracket-quoted segments are parsed with JSON.parse-style unescaping (or similar), so a literal backslash in the property name gets consumed as an escape introducer and there is no escape sequence that yields a literal backslash character in the resulting key.

Reproduction

A data object like { "a\\b": 1 } (key containing a literal backslash) cannot be addressed — any attempt to quote the segment (e.g. $["a\\b"], $['a\\\\b']) either unescapes to a different key or fails to parse to the intended literal key.

Expected

Some way to express a literal backslash in a bracket-quoted property name, e.g. $["a\\\\b"] resolving to the key a\b.

Context

Found while working on json-schema-tools/validator, where schemas may have properties whose names contain backslashes; those subschemas currently cannot be addressed at all.