Move core actions to a subpackage

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

tests/plan/client/filesystem/conflict/test.cue

@@ -2,6 +2,7 @@ package main
 
 import (
 	"dagger.io/dagger"
+	"dagger.io/dagger/core"
 )
 
 dagger.#Plan & {
@@ -11,15 +12,15 @@ dagger.#Plan & {
 		write: contents: actions.test.export.contents
 	}
 	actions: {
-		image: dagger.#Pull & {
+		image: core.#Pull & {
 			source: "alpine:3.15.0@sha256:e7d88de73db3d3fd9b2d63aa7f447a10fd0220b7cbf39803c803f2af9ba256b3"
 		}
 		test: {
-			read: dagger.#Exec & {
+			read: core.#Exec & {
 				input: image.output
 				args: ["echo", client.filesystem."test.txt".read.contents]
 			}
-			write: dagger.#Exec & {
+			write: core.#Exec & {
 				input: image.output
 				args: ["sh", "-c",
 					#"""
@@ -27,7 +28,7 @@ dagger.#Plan & {
 						"""#,
 				]
 			}
-			export: dagger.#ReadFile & {
+			export: core.#ReadFile & {
 				input: write.output
 				path:  "out.txt"
 			}