Refactor library module structure and build configurations
- Moved all source files and resources from the root project into a new 'pdfium' library module.
- Updated build.gradle files to reflect the new module structure.
- Added maven-publish.gradle for publishing the library.
- Added jitpack.yml to specify JDK 17 for JitPack builds.
- Updated .gitignore to exclude build files in the new module.
- Modified gradle.properties to include GROUP_ID and VERSION.
- Changed AndroidManifest.xml in the library module.
- Updated CMakeLists.txt path and include directory.
- Replaced androidx.collection.ArrayMap with android.util.ArrayMap.