Move core actions to a subpackage

Signed-off-by: Helder Correia <174525+helderco@users.noreply.github.com>

pkg/universe.dagger.io/powershell/powershell.cue

@@ -3,6 +3,7 @@ package powershell
 
 import (
 	"dagger.io/dagger"
+	"dagger.io/dagger/core"
 	"universe.dagger.io/docker"
 )
 
@@ -26,7 +27,7 @@ import (
 		contents: string
 
 		_filename: "run.ps1"
-		_write:    dagger.#WriteFile & {
+		_write:    core.#WriteFile & {
 			input:      dagger.#Scratch
 			path:       _filename
 			"contents": contents

pkg/universe.dagger.io/powershell/test/test.cue

@@ -2,6 +2,7 @@ package powershell
 
 import (
 	"dagger.io/dagger"
+	"dagger.io/dagger/core"
 
 	"universe.dagger.io/docker"
 	"universe.dagger.io/powershell"
@@ -19,7 +20,7 @@ dagger.#Plan & {
 		runFile: {
 
 			dir:   _load.output
-			_load: dagger.#Source & {
+			_load: core.#Source & {
 				path: "./data"
 				include: ["*.ps1"]
 			}