Add WithValues to context package and use it in restore.go

Create WithValues in pkg/context/context.go to replace multiple values using
a map. Update runsc/boot/restore.go to use WithValues instead of multiple
WithValue calls.

PiperOrigin-RevId: 914896863

pkg/context/context.go

@@ -254,3 +254,28 @@ func (ctx *withValue) Value(key any) any {
 	}
 	return ctx.Context.Value(key)
 }
+
+// WithValues returns a copy of parent in which the values associated with keys
+// are the corresponding values in the map.
+func WithValues(parent Context, values map[any]any) Context {
+	if len(values) == 0 {
+		return parent
+	}
+	return &withValues{
+		Context: parent,
+		values:  values,
+	}
+}
+
+type withValues struct {
+	Context
+	values map[any]any
+}
+
+// Value implements Context.Value.
+func (ctx *withValues) Value(key any) any {
+	if val, ok := ctx.values[key]; ok {
+		return val
+	}
+	return ctx.Context.Value(key)
+}

runsc/boot/restore.go

@@ -260,10 +260,12 @@ func (r *restorer) restore(l *Loader) error {
 
 	log.Debugf("Restore using fdmap: %#v", fdmap)
 	ctx := l.k.SupervisorContext()
-	ctx = context.WithValue(ctx, vfs.CtxRestoreFilesystemFDMap, fdmap)
 	log.Debugf("Restore using mfmap: %v", mfmap)
-	ctx = context.WithValue(ctx, pgalloc.CtxMemoryFileMap, mfmap)
-	ctx = context.WithValue(ctx, devutil.CtxDevGoferClientProvider, l.k)
+	ctx = context.WithValues(ctx, map[any]any{
+		vfs.CtxRestoreFilesystemFDMap:     fdmap,
+		pgalloc.CtxMemoryFileMap:          mfmap,
+		devutil.CtxDevGoferClientProvider: l.k,
+	})
 
 	if r.asyncMFLoader != nil {
 		// Now that private memory files are known, kick off their loading in the