Add materialAlertDialogTheme to public resources.

Resolves #769

PiperOrigin-RevId: 281547191
(cherry picked from commit 7601cfd)

Author: hunterstich

lib/java/com/google/android/material/dialog/res-public/values/public.xml

@@ -45,6 +45,7 @@
   <public name="ThemeOverlay.MaterialComponents.Dialog.Alert" type="style"/>
   <public name="ThemeOverlay.MaterialComponents.Dialog.Alert.Centered" type="style"/>
 
+  <public name="materialAlertDialogTheme" type="attr"/>
   <public name="materialAlertDialogTitlePanelStyle" type="attr"/>
   <public name="materialAlertDialogTitleIconStyle" type="attr"/>
   <public name="materialAlertDialogTitleTextStyle" type="attr"/>