Add GitHub Action to build debug APK; finalize Android build/tooling and native global fixes

[JacktheRanger]

Motivation

• Ensure the project builds reliably in CI by aligning Android/Gradle tooling and providing an automated workflow that produces a debug APK artifact.
• Fix native linker errors caused by multiple definitions of global JNI and debug variables so native libraries link correctly.

Description

• Added a new GitHub Actions workflow .github/workflows/apk-debug.yml that checks out the repository, sets up JDK 17 and Android SDK, runs ./gradlew :apprts:assembleDebug, and uploads the produced debug APK as an artifact.
• Updated Android build tooling by bumping the Android Gradle Plugin to 7.4.2, pinning the Gradle wrapper to 7.5.1, marking gradlew executable, and consolidating JVM/proxy/truststore settings in gradle.properties.
• Fixed a CMake preprocessor macro quoting issue in libflasher/src/main/cpp/CMakeLists.txt for getlocaledecpoint.
• Resolved duplicate native symbol/linker problems by changing a few global JNI and debug variables to extern in headers and adding a single definition (JavaVM *g_JavaVM = NULL;) in the respective tools.c translation units for libflasher, libmfkey, and libnfc, plus related header adjustments and small cleanup changes.

Testing

• Ran ./gradlew assembleDebug locally as part of the earlier changes which completed successfully and produced apprts/build/outputs/apk/debug/apprts-debug.apk (BUILD SUCCESSFUL).
• The newly added GitHub Actions workflow has been added to the repository but has not been executed in CI (workflow not run).

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