Move core actions to a subpackage

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

tests/tasks/source/source.cue

@@ -2,19 +2,20 @@ package main
 
 import (
 	"dagger.io/dagger"
+	"dagger.io/dagger/core"
 )
 
 dagger.#Plan & {
 	actions: {
-		image: dagger.#Pull & {
+		image: core.#Pull & {
 			source: "alpine:3.15.0@sha256:e7d88de73db3d3fd9b2d63aa7f447a10fd0220b7cbf39803c803f2af9ba256b3"
 		}
 
-		source: dagger.#Source & {
+		source: core.#Source & {
 			path: "."
 		}
 
-		exec: dagger.#Exec & {
+		exec: core.#Exec & {
 			input: image.output
 			mounts: code: {
 				dest:     "/src"
@@ -24,7 +25,7 @@ dagger.#Plan & {
 		}
 
 		test: {
-			verifyHello: dagger.#ReadFile & {
+			verifyHello: core.#ReadFile & {
 				input: source.output
 				path:  "/world.txt"
 			} & {
@@ -32,7 +33,7 @@ dagger.#Plan & {
 				contents: "world\n"
 			}
 
-			verifyWorld: dagger.#ReadFile & {
+			verifyWorld: core.#ReadFile & {
 				input: exec.output
 				path:  "/test.txt"
 			} & {