Fix formatting of BackupEligibilityRules and test

This is a pure refactor, just running `google-java-format --aosp` on
these files and fixing a minor typo in a comment.

Bug: 432673356
Test: builds successfully
Test: atest BackupEligibilityTest
Flag: EXEMPT refactor

Change-Id: I5f42e86e1187bf709537a8fd0c84a81fe3c20a73