Incorporate new Lookup code into VRL and vector

[blt]

The work done in #5374 shows that it's possible to dramatically speed up certain vector workloads and this is something we'd like to achieve. Unfortunately #5374 is a very large pull request and is quite challenging to keep maintained or interrogate, consider that we have also demonstrated that the work done there regresses some workloads to an almost equal degree as the speedup.

So. We want the Lookup/LookupBuf concept integrated into VRL and vector but we don't want to harm our users while doing it. This epic supplants #5374 and is complete when that work is achieved, but through gradual iteration.

Tasks:

• Implement new / fast lookup code, and replace PathIter with it.
• Add support for negative indices
• Move new lookup implementations to Value. Some are still in vector-core::event::util
• Check lookup path syntax at compile time #13033
• Either add support for coalescing to the new lookup code, or remove support from VRL. (Coalescing was added)
• Replace VRL lookup code with the new lookup code.
• Panic in decoding when log_schema.message_key is None #17935
• Refactor value insertions for LogEvent and TraceEvent #18059
• Ensure that configs with message_key set to "" does not cause panics #18104