Lexical: Added ui container type

Structured UI logical to be fairly standard and mostly covered via
a base class that handles context and core dom work.

resources/js/wysiwyg/ui/framework/base-elements.ts

@@ -0,0 +1,39 @@
+import {BaseSelection, LexicalEditor} from "lexical";
+
+export type EditorUiStateUpdate = {
+    editor: LexicalEditor,
+    selection: BaseSelection|null,
+};
+
+export type EditorUiContext = {
+    editor: LexicalEditor,
+};
+
+export abstract class EditorUiElement {
+    protected dom: HTMLElement|null = null;
+    private context: EditorUiContext|null = null;
+
+    protected abstract buildDOM(): HTMLElement;
+
+    setContext(context: EditorUiContext): void {
+        this.context = context;
+    }
+
+    getContext(): EditorUiContext {
+        if (this.context === null) {
+            throw new Error('Attempted to use EditorUIContext before it has been set');
+        }
+
+        return this.context;
+    }
+
+    getDOMElement(): HTMLElement {
+        if (!this.dom) {
+            this.dom = this.buildDOM();
+        }
+
+        return this.dom;
+    }
+
+    abstract updateState(state: EditorUiStateUpdate): void;
+}