Move core actions to a subpackage

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

tests/tasks/diff/diff.cue

@@ -2,18 +2,19 @@ package main
 
 import (
 	"dagger.io/dagger"
+	"dagger.io/dagger/core"
 )
 
 dagger.#Plan & {
 	actions: {
-		alpineBase: dagger.#Pull & {
+		alpineBase: core.#Pull & {
 			source: "alpine:3.15.0@sha256:e7d88de73db3d3fd9b2d63aa7f447a10fd0220b7cbf39803c803f2af9ba256b3"
 		}
-		busyboxBase: dagger.#Pull & {
+		busyboxBase: core.#Pull & {
 			source: "busybox:1.34.1@sha256:1286c6d3c393023ef93c247724a6a2d665528144ffe07bacb741cc2b4edfefad"
 		}
 
-		exec1: dagger.#Exec & {
+		exec1: core.#Exec & {
 			input: alpineBase.output
 			args: [
 				"sh", "-c",
@@ -23,7 +24,7 @@ dagger.#Plan & {
 			]
 		}
 
-		exec2: dagger.#Exec & {
+		exec2: core.#Exec & {
 			input: exec1.output
 			args: [
 				"sh", "-c",
@@ -33,46 +34,46 @@ dagger.#Plan & {
 			]
 		}
 
-		removeme: dagger.#WriteFile & {
+		removeme: core.#WriteFile & {
 			input:    dagger.#Scratch
 			path:     "/removeme"
 			contents: "removeme"
 		}
 
 		test: {
-			diff: dagger.#Diff & {
+			diff: core.#Diff & {
 				lower: alpineBase.output
 				upper: exec2.output
 			}
 
-			verify_diff_foo: dagger.#ReadFile & {
+			verify_diff_foo: core.#ReadFile & {
 				input: diff.output
 				path:  "/dir/foo"
 			} & {
 				contents: "foo"
 			}
-			verify_diff_bar: dagger.#ReadFile & {
+			verify_diff_bar: core.#ReadFile & {
 				input: diff.output
 				path:  "/dir/bar"
 			} & {
 				contents: "bar"
 			}
 
-			mergediff: dagger.#Merge & {
+			mergediff: core.#Merge & {
 				inputs: [
 					busyboxBase.output,
 					removeme.output,
 					diff.output,
 				]
 			}
-			verify_remove: dagger.#Exec & {
+			verify_remove: core.#Exec & {
 				input: mergediff.output
 				args: ["test", "!", "-e", "/removeme"]
 			}
-			verify_no_alpine_base: dagger.#Exec & {
+			verify_no_alpine_base: core.#Exec & {
 				input: mergediff.output
 				// make sure the the Diff actually separated files from the base
-				// by testing the non-existence of a file that only exists in the 
+				// by testing the non-existence of a file that only exists in the
 				// alpine base, not busybox
 				args: ["test", "!", "-e", "/etc/alpine-release"]
 			}