Change Details

As part of the new add users list ui we have a header section with two parts: a text to show how many users were selected and a clear all button. This diff introduces the structure for this header section and the selection text, and a subsquent diff will handle the clear all button logic Linear task: https://linear.app/comm/issue/ENG-5960/selected-users-section Depends on D10743

**PLEASE NOTE THAT THIS DIFF AND SUBSEQUENT DIFFS IN THIS STACK WILL NOT BE LANDED UNTIL MORE OF THE REDESIGN IS READY SINCE THIS WILL CAUSE REGRESSIONS IN PROD** As part of the new add users list ui we have a header section with two parts: a text to show how many users were selected and a clear all button. This diff introduces the structure for this header section and the selection text, and a subsquent diff will handle the clear all button logic Linear task: https://linear.app/comm/issue/ENG-5960/selected-users-section Depends on D10743

**PLEASE NOTE THAT THIS DIFF AND SUBSEQUENT DIFFS IN THIS STACK WILL NOT BE LANDED UNTIL MORE OF THE REDESIGN IS READY SINCE THIS WILL CAUSE REGRESSIONS IN PROD** As part of the new add users list ui we have a header section with two parts: a text to show how many users were selected and a clear all button. This diff introduces the structure for this header section and the selection text, and a subsquent diff will handle the clear all button logic Linear task: https://linear.app/comm/issue/ENG-5960/selected-users-section Depends on D10743