Make js-sdk imports consistent (#2590)

We need to be consistent about whether we import matrix-js-sdk from `src` or
`lib`, otherwise we get two copies of matrix-js-sdk, and everything explodes.

src/analytics/PosthogAnalytics.ts

@@ -16,7 +16,7 @@ limitations under the License.
 
 import posthog, { CaptureOptions, PostHog, Properties } from "posthog-js";
 import { logger } from "matrix-js-sdk/src/logger";
-import { MatrixClient } from "matrix-js-sdk";
+import { MatrixClient } from "matrix-js-sdk/src/matrix";
 import { Buffer } from "buffer";
 
 import { widget } from "../widget";