message: Prevent backspace and delete functionality in the in-call dial pad.
  Just as one cannot do when there inputting number while
  on a call on their phone, it doesn't make much sense to
  be able to do so while on a call in Element. The DTMF
  tone history should be preserved.
diff: @@ -49,6 +49,13 @@ export default class DialpadContextMenu extends React.Component<IProps, IState>
  this.props.onFinished();
  };
  + onKeyDown = (ev) => {
  + // Prevent Backspace and Delete keys from functioning in the entry field
  + if (ev.code === "Backspace" || ev.code === "Delete") {
  + ev.preventDefault();
  + }
  + };
  +
  onChange = (ev) => {
  this.setState({ value: ev.target.value });
  };
  @@ -64,6 +71,7 @@ export default class DialpadContextMenu extends React.Component<IProps, IState>
  className="mx_DialPadContextMenu_dialled"
  value={this.state.value}
  autoFocus={true}
  + onKeyDown={this.onKeyDown}
  onChange={this.onChange}
  />
  </div>
  