Updates BannerMessagePreference to new style

Updates the style of the BannerMessagePreference in v31 and adds support
for the following new functionality (all optional):
- Use one of three attention level themes: high, medium, and low
(default: high)
- Add an icon (default: alert icon)
- Subtitle (default: hidden)
- Dismiss button (default: hidden)

Icon, subtitle, and theme can also be set via xml attrs.

Adds support for creating a BannerMessage without a title.

Test: make -j80 RunSettingsLibRoboTests
Test: Manually tested all configurations
Bug: 181764215

Change-Id: I73bfc5225d83057e423b6a9d77a6277a656d3b90
diff --git a/packages/SettingsLib/BannerMessagePreference/AndroidManifest.xml b/packages/SettingsLib/BannerMessagePreference/AndroidManifest.xml
index 56b886f..dd51ea3 100644
--- a/packages/SettingsLib/BannerMessagePreference/AndroidManifest.xml
+++ b/packages/SettingsLib/BannerMessagePreference/AndroidManifest.xml
@@ -18,6 +18,6 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
           package="com.android.settingslib.widget">
 
-    <uses-sdk android:minSdkVersion="21"/>
+    <uses-sdk android:minSdkVersion="28"/>
 
 </manifest>