feat: merge manifest resolutions and pnpm.overrides (#7174)

* feat: merge manifest `resolutions` and `pnpm.overrides`

As someone currently migrating from Yarn, I would find it extremely
helpful to be able to give Yarn and pnpm different override
instructions.

By merging these two, migration from Yarn is even easier, because you
can fix pnpm-specific overrides inside `pnpm.overrides` without
affecting the existing Yarn setup.

* style: make changeset just one line

* Update .changeset/twenty-walls-sit.md

---------

Co-authored-by: Zoltan Kochan <z@kochan.io>

.changeset/twenty-walls-sit.md

@@ -0,0 +1,6 @@
+---
+"@pnpm/config": patch
+"pnpm": patch
+---
+
+Instead of `pnpm.overrides` replacing `resolutions`, the two are now merged. This is intended to make it easier to migrate from Yarn by allowing one to keep using `resolutions` for Yarn, but adding additional changes just for pnpm using `pnpm.overrides`.

config/config/src/getOptionsFromRootManifest.ts

@@ -26,7 +26,10 @@ export function getOptionsFromRootManifest (manifestDir: string, manifest: Proje
   // so we cannot call it resolutions
   const overrides = mapValues(
     createVersionReferencesReplacer(manifest),
-    manifest.pnpm?.overrides ?? manifest.resolutions ?? {}
+    {
+      ...manifest.resolutions,
+      ...manifest.pnpm?.overrides,
+    }
   )
   const neverBuiltDependencies = manifest.pnpm?.neverBuiltDependencies
   const onlyBuiltDependencies = manifest.pnpm?.onlyBuiltDependencies