refactor: use pnpm file: id field (#2449)

... and add a `fail` in the `if` where we extract all info from the key
and are assuming there is no explicit `name/version/id`. If this `fail`
is ever hit we should fix it.

### Changes are visible to end-users: no

### Test plan

- Covered by existing test cases

Author: jbedard

e2e/pnpm_lockfiles/projects/c/package.json

@@ -4,6 +4,9 @@
     "dependencies": {
         "@scoped/a": "link:../a"
     },
+    "devDependencies": {
+        "a-types": "file:../a-types"
+    },
     "peerDependencies": {
         "@scoped/b": "workspace:*"
     }