Extract LegacyDelegate and ElementInternalsDelegate

Delegate implementation-specific methods and properties to the
appropriate delegate. Set the delegate based on the
`TrixEditorElement.formAssociated` property.

src/test/system/accessibility_test.js

@@ -1,33 +1,34 @@
-import { assert, test, testGroup, triggerEvent } from "test/test_helper"
+import { assert, skipIf, test, testGroup, triggerEvent } from "test/test_helper"
+import TrixEditorElement from "trix/elements/trix_editor_element"
 
 testGroup("Accessibility attributes", { template: "editor_default_aria_label" }, () => {
   test("sets the role to textbox", () => {
     const editor = document.getElementById("editor-without-labels")
     assert.equal(editor.getAttribute("role"), "textbox")
   })
 
-  test("does not set aria-label when the element has no <label> elements", () => {
+  skipIf(TrixEditorElement.formAssociated, "does not set aria-label when the element has no <label> elements", () => {
     const editor = document.getElementById("editor-without-labels")
     assert.equal(editor.hasAttribute("aria-label"), false)
   })
 
-  test("does not override aria-label when the element declares it", () => {
+  skipIf(TrixEditorElement.formAssociated, "does not override aria-label when the element declares it", () => {
     const editor = document.getElementById("editor-with-aria-label")
     assert.equal(editor.getAttribute("aria-label"), "ARIA Label text")
   })
 
-  test("does not set aria-label when the element declares aria-labelledby", () => {
+  skipIf(TrixEditorElement.formAssociated, "does not set aria-label when the element declares aria-labelledby", () => {
     const editor = document.getElementById("editor-with-aria-labelledby")
     assert.equal(editor.hasAttribute("aria-label"), false)
     assert.equal(editor.getAttribute("aria-labelledby"), "aria-labelledby-id")
   })
 
-  test("assigns aria-label to the text of the element's <label> elements", () => {
+  skipIf(TrixEditorElement.formAssociated, "assigns aria-label to the text of the element's <label> elements", () => {
     const editor = document.getElementById("editor-with-labels")
     assert.equal(editor.getAttribute("aria-label"), "Label 1 Label 2 Label 3")
   })
 
-  test("updates the aria-label on focus", () => {
+  skipIf(TrixEditorElement.formAssociated, "updates the aria-label on focus", () => {
     const editor = document.getElementById("editor-with-modified-label")
     const label = document.getElementById("modified-label")
 

src/test/test_helpers/test_helpers.js

@@ -48,6 +48,10 @@ export const testGroup = function (name, options, callback) {
   }
 }
 
+export const skipIf = function (condition, ...args) {
+  testIf(!condition, ...args)
+}
+
 export const testIf = function (condition, ...args) {
   if (condition) {
     test(...Array.from(args || []))