[Doc][TopAppBar] Detailed description of code example for collapsing …

…toolbar style

Resolves #3915

GIT_ORIGIN_REV_ID=88bb0c690dc9fb8386165acfffcf9d18ae897f1d
PiperOrigin-RevId: 601582020

(cherry picked from commit b80efdd)

docs/components/TopAppBar.md

@@ -496,6 +496,8 @@ In the layout:
 
  <com.google.android.material.appbar.MaterialToolbar
  ...
+ android:layout_width="match_parent"
+ android:layout_height="?attr/actionBarSize"
  android:elevation="0dp" />
 
  </com.google.android.material.appbar.CollapsingToolbarLayout>
@@ -533,6 +535,8 @@ In the layout:
  android:layout_height="?attr/collapsingToolbarLayoutLargeSize">
 
  <com.google.android.material.appbar.MaterialToolbar
+ android:layout_width="match_parent"
+ android:layout_height="?attr/actionBarSize"
  ...
  android:elevation="0dp" />
 
@@ -580,6 +584,8 @@ In the layout:
  android:contentDescription="@string/content_description_media" />
 
  <com.google.android.material.appbar.MaterialToolbar
+ android:layout_width="match_parent"
+ android:layout_height="?attr/actionBarSize"
  ...
  android:background="@android:color/transparent" />
 
@@ -623,6 +629,7 @@ In the layout:
 
  <com.google.android.material.appbar.MaterialToolbar
  ...
+ android:layout_height="?attr/actionBarSize"
  app:layout_collapseMode="pin"
  />