[tests] Fix Layout so the test app actually runs (dotnet#2720)

Currently when running the `Mono.Android-Test` app we get the
following error:

	Java.Lang.RuntimeException: Binary XML file line #1: You must supply a layout_width attribute.

This is because `ScrollView` now needs to have the properties
`//@android:layout_width` and `//@android:layout_height`.  Once we
provide those, we then get:

	Scrollview can host only one direct child

We then need to add a `LinearLayout` to the `ScrollView` so that it
removes that error as well.

src/Mono.Android/Test/Resources/layout/Main.axml

@@ -18,19 +18,26 @@
       android:editable="false"
   />
   <ScrollView
-      android:id="@+id/my_scroll_view">
-    <TextView
-        android:id="@+id/first_text_view"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:editable="false"
-    />
-    <TextView
-        android:id="@+id/second_text_view"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:editable="false"
-    />
+      android:id="@+id/my_scroll_view"
+      android:layout_width="fill_parent"
+      android:layout_height="fill_parent">
+    <LinearLayout
+        android:orientation="vertical"
+        android:layout_width="fill_parent"
+        android:layout_height="fill_parent">
+      <TextView
+          android:id="@+id/first_text_view"
+          android:layout_width="wrap_content"
+          android:layout_height="wrap_content"
+          android:editable="false"
+      />
+      <TextView
+          android:id="@+id/second_text_view"
+          android:layout_width="wrap_content"
+          android:layout_height="wrap_content"
+          android:editable="false"
+      />
+    </LinearLayout>
   </ScrollView>
 
   <fragment

tests/Runtime-MultiDex/Mono.Android-TestsMultiDex.csproj

@@ -75,6 +75,14 @@
       <Link>Resources\Drawable\Image.9.png</Link>
     </AndroidResource>
   </ItemGroup>
+  <ItemGroup>
+    <AndroidAsset Include="..\..\src\Mono.Android\Test\Assets\asset1.txt">
+      <Link>Assets\asset1.txt</Link>
+    </AndroidAsset>
+    <AndroidAsset Include="..\..\src\Mono.Android\Test\Assets\subfolder\asset2.txt">
+      <Link>Assets\subfolder\asset2.txt</Link>
+    </AndroidAsset>
+  </ItemGroup>
   <Import Project="$(MSBuildExtensionsPath)\Xamarin\Android\Xamarin.Android.CSharp.targets" />
   <Import Project="Mono.Android-TestsMultiDex.targets" />
   <ItemGroup>

tests/Runtime-MultiDex/Resources/layout/Main.axml

@@ -18,19 +18,26 @@
       android:editable="false"
   />
   <ScrollView
-      android:id="@+id/my_scroll_view">
-    <TextView
-        android:id="@+id/first_text_view"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:editable="false"
-    />
-    <TextView
-        android:id="@+id/second_text_view"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:editable="false"
-    />
+      android:id="@+id/my_scroll_view"
+      android:layout_width="fill_parent"
+      android:layout_height="fill_parent">
+    <LinearLayout
+        android:orientation="vertical"
+        android:layout_width="fill_parent"
+        android:layout_height="fill_parent">
+      <TextView
+          android:id="@+id/first_text_view"
+          android:layout_width="wrap_content"
+          android:layout_height="wrap_content"
+          android:editable="false"
+      />
+      <TextView
+          android:id="@+id/second_text_view"
+          android:layout_width="wrap_content"
+          android:layout_height="wrap_content"
+          android:editable="false"
+      />
+    </LinearLayout>
   </ScrollView>
 
   <fragment