Apply dialog style to User switcher dialog.

Apply the unified style and set just the inner content, relying on the
default title and buttons.

Also, fix using the vertical spacing in PseudoGridView.

Test: manual
Test: atest UserSwitchDialogControllerTest
Bug: 203666386
Change-Id: If6a0220979d9f9df584c29f4adce317341577cf4
Merged-In: If6a0220979d9f9df584c29f4adce317341577cf4