Scaffold out basic IDL for revamped scoped registry

This implements the IDL definitions per the spec issue[1], however
all methods are basic stubs and do not execute any logic - the logic
will come with later patches.

I2P: https://groups.google.com/a/chromium.org/g/blink-dev/c/um-9YjJWyEQ/m/MhKN0L7FAgAJ

Spec PRs:

HTML: whatwg/html#10869
DOM: whatwg/dom#1341

[1]: whatwg/html#10854

Bug: 409577162
Change-Id: Ieee709ff15c13bdd0b1d7598e27031867062b592
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6443776
Reviewed-by: David Baron <[email protected]>
Commit-Queue: Keith Cirkel <[email protected]>
Commit-Queue: David Baron <[email protected]>
Auto-Submit: Keith Cirkel <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1446589}

Author: keithamus

custom-elements/revamped-scoped-registry/idlharness.tentative.window.js

@@ -0,0 +1,21 @@
+// META: script=/resources/WebIDLParser.js
+// META: script=/resources/idlharness.js
+// META: global=window,dedicatedworker,shadowrealm-in-window
+
+idl_test(
+  ["scoped-custom-elements-registry.tentative"],
+  ["html", "dom"],
+  (idl_array) => {
+    let element = document.createElement("div");
+    let shadowRoot = element.attachShadow({ mode: "open" });
+    let customElementRegistry = new CustomElementRegistry();
+    let templateElement = document.createElement("template");
+    idl_array.add_objects({
+      document,
+      element,
+      shadowRoot,
+      customElementRegistry,
+      templateElement,
+    });
+  },
+);

interfaces/scoped-custom-elements-registry.tentative.idl

@@ -0,0 +1,38 @@
+[Exposed=Window]
+partial interface CustomElementRegistry {
+  constructor();
+  undefined initialize(Node root);
+};
+
+[Exposed=Window]
+partial interface HTMLTemplateElement {
+  [CEReactions] attribute DOMString shadowRootCustomElementRegistry;
+};
+
+[Exposed=Window]
+partial interface Document {
+  readonly attribute CustomElementRegistry? customElementRegistry;
+};
+
+[Exposed=Window]
+partial interface Element {
+  readonly attribute CustomElementRegistry? customElementRegistry;
+};
+
+[Exposed=Window]
+partial interface ShadowRoot {
+  readonly attribute CustomElementRegistry? customElementRegistry;
+};
+
+dictionary ImportNodeOptions {
+  CustomElementRegistry customElementRegistry;
+  boolean selfOnly = false;
+};
+
+partial dictionary ShadowRootInit {
+  CustomElementRegistry customElementRegistry;
+};
+
+partial dictionary ElementCreationOptions {
+  CustomElementRegistry customElementRegistry;
+};