Add rounded corners to bottom sheet dialog.

Note these are currently only visible in the collapsed state.
- [Google issue](https://issuetracker.google.com/issues/144859239)
- [Rejected PR](material-components/material-components-android#437)
- [Github issue](material-components/material-components-android#1278)

Author: jonnyandrew

library/ui-styles/src/main/res/values/styles_bottom_sheet.xml

@@ -14,6 +14,7 @@
         <!-- Default color for text View -->
         <item name="android:textColorTertiary">@color/element_content_primary_light</item>
         <item name="android:textColorLink">@color/element_link_light</item>
+        <item name="bottomSheetStyle">@style/BottomSheetStyle</item>
     </style>
 
     <style name="Theme.Vector.BottomSheetDialog.Dark" parent="Theme.MaterialComponents.BottomSheetDialog">
@@ -28,13 +29,23 @@
         <!-- Default color for text View -->
         <item name="android:textColorTertiary">@color/element_content_primary_dark</item>
         <item name="android:textColorLink">@color/element_link_dark</item>
+        <item name="bottomSheetStyle">@style/BottomSheetStyle</item>
     </style>
 
     <style name="Theme.Vector.BottomSheetDialog.Black" parent="Theme.Vector.BottomSheetDialog.Dark">
         <item name="colorSurface">@color/element_background_black</item>
     </style>
 
     <!-- BottomSheet style -->
+    <style name="BottomSheetStyle" parent="Widget.MaterialComponents.BottomSheet.Modal">
+        <item name="shapeAppearance">@style/BottomSheetShapeAppearance</item>
+    </style>
+
+    <style name="BottomSheetShapeAppearance" parent="">
+        <item name="cornerFamily">rounded</item>
+        <item name="cornerSize">20dp</item>
+    </style>
+
     <style name="BottomSheetItemTextMain">
         <item name="android:fontFamily">sans-serif-medium</item>
         <item name="android:layout_width">0dp</item>

vector/src/main/res/layout/bottom_sheet_attachment_type_selector.xml

@@ -3,7 +3,6 @@
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:background="?colorSurface"
     android:orientation="vertical">
 
     <androidx.core.widget.NestedScrollView

vector/src/main/res/layout/view_bottom_sheet_action_button.xml

@@ -10,7 +10,6 @@
         android:id="@+id/bottomSheetActionClickableZone"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
-        android:background="?colorSurface"
         android:clickable="true"
         android:focusable="true"
         android:foreground="?attr/selectableItemBackground"
@@ -93,4 +92,4 @@
 
     </androidx.constraintlayout.widget.ConstraintLayout>
 
-</merge>
+</merge>