Add FEEL errors to linting

[marstamm]

Epic: https://github.com/camunda/product-hub/issues/280

• Create feel-linter library which exports Codemirror Component and String linter: https://github.com/bpmn-io/feel-lint
• Integrate it into default lint rules: Add FEEL errors to linting #22
• perform Performance test for complex diagrams, introduce caching if performance is bad
• Align Error message style with VS Code

Follow-ups:
bpmn-io/properties-panel#190

[CatalinaMoisuc]

@marstamm please open an integration issue in the Web Modeler repository.

As discussed, maybe just a version bump is enough.

[marstamm]

Performance

• Adding FEEL expression Linting adds ~0.1 ms linting time per expression
• Because linting is done synchronously, this can cause lag when modeling

When tested with a 2.000 expression diagram, the lag was noticable but still usable. I think the performance impact is still small enough that we can open the base PRs without performance improvements.

Still, I would like to look into into caching now, so we have a solid foundation when we want to introduce Variable null checks and other more resource intensive linting rules

[marstamm]

Caching Spike results

Caching creates the challenge of creating hashes for the Objects, so we can figure out if they changed in the next run. We need to do this not only for the Element itself but for the complete subtree, as some lint rules access extension elements while others are using the child elements directly.

While I was able to build working caching, the performance is worse than running linting normally and adds time for every element.

Instead of caching, we could think about linting changes only, e.g. by integrating into eventBus events. This would require a bigger refactoring, so I will not pursue it further now.

[marstamm]

done via #31