Elevate Java version to 17

[neboskreb]

As of August 31, 2025 all apks published to Play store must have targetSdk at 35 or higher, which means that the minimal Java version is now 17. Hence we can elevate JAVA_VERSION setting in build.gradle to 17 without losing any compatibility.

[neboskreb]

Question: what if a library project targeting Java 11 wants to employ android-log4j2 in their tests? Will its Java 17 requirement become a breaking factor?

Rationale: Android libraries are not published to Play Store, therefore they are not bound with the requirement to target API 35. They can be used in "legacy" projects which legitimately target older API, hence older Java version. If we require min Java 17 will it lock such users out?