New user switcher dialog

This dialog will eventually replace the UserDetailView. Right now, it
uses the same adapter to display the content (which is not necessarily
bad).

Missing:
  * Red lines (including landscape size).
  * Bring user circles up to spec (once it's finalized).
  * Launch animations (to and from dialog).

Test: manual
Test: atest SystemUITests
Bug: 185360864
Bug: 198796184

Change-Id: I903d111822d1958fb53c43932b2df1393c841c71
Merged-In: I903d111822d1958fb53c43932b2df1393c841c71
Merged-In: I624169c76e4c9efa30d922235616190666ae949e
Merged-In: I2b4082dd65f06d2d08706ac3db017ac1495aefed