Add a module API for overriding the composer preview. (#33978)

* Modify LinkPreview to export shared atomics

* Implement MessageComposerUrlPreviewView

* Create UrlPreviewFetcher utility function

* Modify view models

* Implement in composer

* Support running tests in dom-less vitest environment

* Add a playwright test

* hide another one

* fmt

* cleanup

* test rte too

* fixup

* Add back docstring

* cleanup

* off by one

* remove description check

* Cleanup hacks

* Remove another hack

* cleanup

* one more

* fixup window here too

* whoops type

* Rename to be cleaeer

* Trim URLs first

* fix bug

* Add a module API for overriding the composer preview.

* tests + cleanup

* fixup comment

* revert accidental change

* fixup

* happy tests

* cleanup

packages/module-api/element-web-module-api.api.md

@@ -146,11 +146,26 @@ export type Container = "top" | "right" | "center";
 
 // @alpha
 export interface CustomComponentsApi {
+    registerComposerPreview(filterFn: (composerText: string, roomId: string) => boolean, renderer: CustomComposerPreviewRenderFunction): void;
     registerLoginComponent(renderer: CustomLoginRenderFunction): void;
     registerMessageRenderer(eventTypeOrFilter: string | ((mxEvent: MatrixEvent) => boolean), renderer: CustomMessageRenderFunction, hints?: CustomMessageRenderHints): void;
     registerRoomPreviewBar(renderer: CustomRoomPreviewBarRenderFunction): void;
 }
 
+// @alpha
+export type CustomComposerPreviewComponentProps = {
+    text: string;
+    roomId: string;
+    target?: ComposerApiTarget;
+    relation?: {
+        inReplyToEventId?: string;
+        relType?: string;
+    };
+};
+
+// @alpha
+export type CustomComposerPreviewRenderFunction = ExtendablePropsRenderFunction<CustomComposerPreviewComponentProps>;
+
 // @alpha
 export interface CustomisationsApi {
     registerShouldShowComponent(fn: (this: void, component: UIComponent) => boolean | void): void;