Flexible document editing and building strategy

[raylras]

In projects with ~1400 DSL files, editing one document can trigger up to 650 rebuilds, slowing down auto-completion.

To address this, I modified relinking to skip some steps, which impacts timely diagnostics. See intellizen-dev/intellizen#90 .

Since different languages have unique needs, I suggest Langium provide more default document building strategies. Some of my thoughts:

interface OnDocumentChangeStrategy {
  changed: (docs: LangiumDocument[]) => void
  // means 'opened' or 'synced'
  frontend: (docs: LangiumDocument[]) => void
  backend: (docs: LangiumDocument[]) => void
}

const Slowest: OnDocumentChangeStrategy = {
  changed: docs => buildDocumentsTo(docs, DocumentState.Validated),
  frontend: docs => buildDocumentsTo(docs.filter(isAffected), DocumentState.Validated),
  backend: docs => buildDocumentsTo(docs.filter(isAffected), DocumentState.Validated),
}

const Medium: OnDocumentChangeStrategy = {
  changed: docs => buildDocumentsTo(docs, DocumentState.Validated),
  frontend: docs => buildDocumentsTo(docs.filter(isAffected), DocumentState.Validated),
  backend: docs => relinkDocuments(docs),
}

const Fastest: OnDocumentChangeStrategy = {
  changed: docs => buildDocumentsTo(docs, DocumentState.Validated),
  frontend: docs => { /* NO-OP */ },
  backend: docs => { /* NO-OP */ },
}

Is there a better way to approach this? Any suggestions would be greatly appreciated.