Gradle build refactoring and version upgrade (6 to 8) 🚀🚀

[dejan2609]

Note: dependencies versions are not changed (i.e. only the build logic is improved/refactored).

details:

• gradle version upgrade: 6.8.2 -->> 8.11.1
• 'launch4j' plugin upgrade: 2.4.9 -->> 3.0.6
• 'shadow' plugin is introduced (in order to replace 'fatJar' task and to simplify gradle build): https://github.com/GradleUp/shadow
• dependencies configurations are changed (note that dependencies versions are left intact):
  • 'compile' is replaced with 'implementation'
  • 'testCompile' is replaced with 'testImplementation'
  • 'sourceCompatibility' is removed in favor of 'toolchain'
  • Java project compatibility version is bumped from 7 to 8 (note: Gradle build JDK required version is >=8, i.e. 8, 11, 17, 21, etc.)
  • checksum verification for Gradle distribution is added (using 'distributionSha256Sum' property in 'gradle-wrapper.properties')

related links:

• https://docs.gradle.org/8.11.1/userguide/upgrading_version_6.html#sec:configuration_removal
• https://docs.gradle.org/8.11.1/userguide/upgrading_version_7.html#wrapper_task_configuration
• https://docs.gradle.org/8.11.1/userguide/upgrading_version_8.html#java_convention_deprecation
• https://docs.gradle.org/8.11.1/userguide/gradle_wrapper.html#configuring_checksum_verification
• https://docs.gradle.org/8.11.1/userguide/toolchains.html
• https://docs.gradle.org/8.11.1/dsl/org.gradle.api.plugins.JavaPluginExtension.html#org.gradle.api.plugins.JavaPluginExtension:toolchain