Screen Capture: Create blank and closable toolbar in Compose

Creates a blank toolbar container which will hold all the control
components. The toolbar has a leading close button which will
eventually handle dimissing the toolbar.

Bug: 412723197, 412722802
Test: Manual
Flag: com.android.systemui.desktop_screen_capture
Change-Id: I0e07bd3dd737bf5a77778af766c007849eed85df