Fallback parsing of literals as strings is invalid and inconsistent

[gibson042]

https://jmespath.org/specification.html#grammar and https://jmespath.site/#spec-grammar both require a `…` literal to contain a valid JSON value. tokenize('`[x]`') accordingly throws a SyntaxError, but expressions like tokenize('`x`') and tokenize('`0x`') and tokenize('`Infinity`') incorrectly return a Literal.

If support for "the old syntax of allowing elided quotes in JSON literal expressions" is intentional, then it should be consistent and should also come with a deprecation warning (cf. JEP-12).