Support non-quoted integer path segments

[ktff]

Enable usage of non-quoted integers in path segments. Some examples would be .0, .field.12, .2.label etc...

vectordotdev/vector#7045 enabled usage of non-quoted path identifiers that start with a number. Originally, support for non-quoted integers as path segments was also planned but was scraped once the issues around it became clear and it's usefulness was questioned.

Issue

Main issue is _ chars in integers. Currently the parser will parse 1_000 as an integer and will erase underscores. A naive implementation would use the parsed integer as a key which would result in following { "1_000": "a", "1000": "b"}.1_000 to evaluate as "b".

There are two known approaches:

• Introduce more context into lexer so that it can know when it's in a path so to parse integers as identifiers.
• Raise construction of integers to grammar where we have context.

Both options would introduce quite the complexity for a feature that is at best a nice to have and at worst could introduce more confusion than it would resolve.

Alternatives

Quoted integers are supported, ."0" works, so in the case of not going through with this change no other change is required.

Follow up on vectordotdev/vector#7045, vectordotdev/vector#6780