fix(material/sidenav): fix tabindex issue on side mode

[DBowen33]

remove tabindex=-1 from mat-drawer when in mode="side" so that the mat-drawer container it is not focusable by mobile screen readers such as TalkBack

Before Screencast: https://screencast.googleplex.com/cast/NTYzNjAxNjE0Nzc5MTg3MnwzOGVlNmNmZC1jYQ After Screencast: https://screencast.googleplex.com/cast/NDg5NzA2MTg1NzEzMjU0NHxjZTcyZGY5MS04OA

fixes b/286459024

[github-actions[bot]]

Deployed dev-app for 51c1075b797fba212ebd5fcec051684970d0083a to: https://ng-dev-previews-comp--pr-angular-components-30979-dev-a2aqsdxi.web.app

Note: As new commits are pushed to this pull request, this link is updated after the preview is rebuilt.