Fix isAtLeastU for post-U codenames

isAtLeastU assumed that unknown codenames were a single letter, which
hasn't been true since Tiramisu. Copy the implementation from the platform's
frameworks/libs/modules-utils/java/com/android/modules/utils/build/SdkLevel.java.

Test: atest --host SettingsGoogleRoboTests
Bug: 264658905
Change-Id: I6311ffe2fce9f337df853b57de3e41b581e263ee
1 file changed