Convert a bunch more js-sdk imports to absolute paths

Turns out a lot of the typescript warnings about improper warnings were correct. TypeScript appears to be pulling in two copies of the js-sdk when we do this, which can lead to type conflicts (or worse: the wrong code entirely). We fix this at the webpack level by explicitly importing from `src`, but some alternative build structures have broken tests because of this - jest ends up pulling in the "wrong" js-sdk, breaking things.

src/components/structures/MatrixChat.tsx

@@ -18,8 +18,7 @@ limitations under the License.
 */
 
 import React, { createRef } from 'react';
-// @ts-ignore - XXX: no idea why this import fails
-import * as Matrix from "matrix-js-sdk";
+import { createClient } from "matrix-js-sdk/src/matrix";
 import { InvalidStoreError } from "matrix-js-sdk/src/errors";
 import { RoomMember } from "matrix-js-sdk/src/models/room-member";
 import { MatrixEvent } from "matrix-js-sdk/src/models/event";
@@ -1649,7 +1648,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             let cli = MatrixClientPeg.get();
             if (!cli) {
                 const {hsUrl, isUrl} = this.props.serverConfig;
-                cli = Matrix.createClient({
+                cli = createClient({
                     baseUrl: hsUrl,
                     idBaseUrl: isUrl,
                 });