[Android] Update Gradle version for compatibility with latest Java releases, and fix deprecation warnings
Moved the target SDK version to 35, as per Google Play policies and especially avoiding the "this app was built for an older version of Android" warning. Targeting for Java 8 is deprecated on releases 24 and up. Also fixed other Gradle-related deprecation warnings.
Unfortunately, we can't do that yet. Updating API version means breaking the built-in file picker as the old storage permission no longer works for "security" reasons - instead, the app has to receive a new "Manage Storage" permission which may disqualify it from Play Store approval as Furnace does not meet the criteria for apps with the aforementioned permission (file managers, security, backup or similar).
Before I can merge this pull request, full support for Android's file API has to be added, including system file dialogs. This has the benefit of allowing us to read and write on non-storage locations, such as other apps' storage or cloud services.
What about just the Gradle-related changes first? Otherwise, errors occur when building using the latest Java versions
Now undid the Play Protect thing, to where it's only just compatibility with current Java versions and fixing deprecation warnings when building for Android