[expressions][kql] Migrate from PEG.js to new "Peggy" fork.

[lukeelmers]

As discussed in this issue, development of the PEG.js library has stalled as the maintainer has abandoned the project.

A new fork named Peggy has been created and community members are being encouraged to migrate to it.

If we plan to keep the PEG-based implementation of KQL and Expressions for the foreseeable future, we should consider migrating to the fork so that we can keep getting updates.

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServices)

[wylieconlon]

We also use this for tinymath and the work on the Lens formula system.

[legrego]

@lukeelmers just caught up on the linked PEG.js issue, and I was pleasantly surprised to see that you're one step ahead of me! Thanks for opening this issue so we can track progress on our end 💚

[wylieconlon]

It looks like the fork is fully backwards-compatible, so I prepared a small PR to move tinymath over. I will spend a short time to see if I can migrate all the grammars at once, since I found it quite a small task.

[wylieconlon]

As explained in #17284, this issue is blocked because our build tooling only uses peg.js 0.9.0, so switching libraries would also require upgrading the build. I think that whoever is migrating this would need to move all .peg grammars (timelion, kql, expressions) into packages/*, so that we are able to use Bazel to automatically build these files. We can probably do the peggy migration at the same time as moving the grammars into packages/*