Apply elevation overlay to colored navbar (#6308)

app/src/main/java/com/google/android/material/bottomsheet/BottomSheetBehaviorExtensions.kt

@@ -0,0 +1,10 @@
+package com.google.android.material.bottomsheet
+
+import android.view.View
+
+/**
+ * Returns package-private elevation value
+ */
+fun <T : View> BottomSheetBehavior<T>.getElevation(): Float {
+    return elevation.takeIf { it >= 0F } ?: 0F
+}