Define widget driver as an interface

- Adds `IWidgetDriver` interface
- Renames `WidgetDriver` to `BaseWidgetDriver` with old name (`WidgetDriver`) supported but deprecated

The goal here is to mean that a client that is implementing a driver can more easily see at compile time what is changing between versions.

However, this would mean that we need to change the versioning policy as any addition to IWidgetDriver would be a breaking change (so major version bump). Whereas, at the moment we don't do a major version bump because the abstract WidgetDriver class doesn't require the implementing client to implement anything.

Author: hughns

README.md

@@ -77,7 +77,7 @@ SDK to provide an interface for other platforms.
 TODO: Improve this
 
 ```typescript
-const driver = new CustomDriver(); // an implementation of WidgetDriver
+const driver = new CustomDriver(); // an implementation of IWidgetDriver
 const api = new ClientWidgetApi(widget, iframe, driver);
 
 // The API is automatically started, so we just have to wait for a ready before doing something

src/ClientWidgetApi.ts

@@ -30,7 +30,7 @@ import {
     getTimelineRoomIDFromCapability,
     isTimelineCapability,
 } from "./interfaces/Capabilities";
-import { IOpenIDUpdate, ISendEventDetails, ISendDelayedEventDetails, WidgetDriver } from "./driver/WidgetDriver";
+import { IOpenIDUpdate, ISendEventDetails, ISendDelayedEventDetails, IWidgetDriver } from "./driver/WidgetDriver";
 import {
     ICapabilitiesActionResponseData,
     INotifyCapabilitiesActionRequestData,
@@ -158,12 +158,12 @@ export class ClientWidgetApi extends EventEmitter {
      * conditions, a "ready" event will be raised.
      * @param {Widget} widget The widget to communicate with.
      * @param {HTMLIFrameElement} iframe The iframe the widget is in.
-     * @param {WidgetDriver} driver The driver for this widget/client.
+     * @param {IWidgetDriver} driver The driver for this widget/client.
      */
     public constructor(
         public readonly widget: Widget,
         private iframe: HTMLIFrameElement,
-        private driver: WidgetDriver,
+        private driver: IWidgetDriver,
     ) {
         super();
         if (!iframe?.contentWindow) {