MediaRouter: make group expand/collapse button 48x48
MediaRouter: make group expand/collapse button 48x48

48x48 is android standard for the buttons for touch detection.

Bug: 23118003
Change-Id: I329313c44ac9a3db4b30b1230bb5721b66ce9270

aosp-mirror/platform_frameworks_support,androidx/androidx,androidx/androidx,aosp-mirror/platform_frameworks_support,AndroidX/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,aosp-mirror/platform_frameworks_support,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,aosp-mirror/platform_frameworks_support,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,aosp-mirror/platform_frameworks_support