fix(pnp): handle require.resolve('pnpapi') with exports correctly

[paul-soporan]

What's the problem this PR addresses?

When using PnP, calling require.resolve('pnpapi') tries to apply the exports resolution on the pnpapi path, either remapping it if there's a ".pnp.cjs": "./whatever.js" export (which is wrong) or throwing if there isn't such an export.

We originally considered this in #2431 (comment) but thought it wasn't a problem, even though it actually is - the unqualifiedPath is the one that gets resolved to a path in resolveUnqualifiedExport, not the request.

Fixes #3493.

How did you fix it?

Special-cased pnpapi in resolveRequest with an early return.

Checklist

• I have read the Contributing Guide.

• I have set the packages that need to be released for my changes to be effective.

• I will check that all automated PR checks pass before the PR gets reviewed.