[bc25] Let `OverlayShade` wrap its content, for easier responsiveness.

This will allow each of the caller composables to determine the width
depending on the content, which is useful since NSSL already determines
the notification width itself.

Test: Existing unit tests build and pass.
Bug: 338033836
Flag: com.android.systemui.dual_shade
Change-Id: I75732f785c6f73a912d677cb7578df0443dbba90