Clarify performance impact of project references on ts-server, and recommended usage of 'disableSourceOfProjectReferenceRedirect' or alternatives

[jroitgrund]

From the docs (https://www.typescriptlang.org/tsconfig/#disableSourceOfProjectReferenceRedirect, https://www.typescriptlang.org/docs/handbook/project-references.html), it's clear that:

• project references enable tsc -b for improved type-checking performance
• they can also improve tsserver (and therefore IDE) performance if declaration files are 'pre-emitted' and you enable disableSourceOfProjectReferenceRedirect

In a monorepo, where most change units touch multiple projects, you want the behaviour of disableSourceOfProjectReferenceRedirect: false, ie you don't want to have to manually re-generate declaration files if you're changing a leaf project. Here's what's unclear: how is tsserver (and therefore IDE) performance affected by project references in this case? The docs should clarify:

• whether tsserver performance is expected to improve with project references and disableSourceOfProjectReferenceRedirect: false, compared to without project references?
• if not, whether there is a recommended setup to let tsserver benefit from project references without having to manually regenerate declaration files?

See also https://stackoverflow.com/questions/67093879/are-typescript-project-references-helpful-with-noemit (no real answer) and microsoft/TypeScript#42607 (where according to the last benchmark by the submitter, project references actually slightly worsen performance, even after the patch).