Upgrades:
* Maven Enforcer Plugin to 3.0.0-M3
* Maven Surefire Plugin to 3.0.0-M5
* Maven Checkstyle Plugin to 3.1.1
* Maven Bundle Plugin to 5.1.1
* Jacoco Maven Plugin to 0.8.6
* Checkstyle to 8.36.1
* JUnit Jipiter to 5.7.0
* AssertJ to 3.17.2
* Guava to 29.0-jre
Fix AssertJ breaking changes
Use Java 8 or Apache Commons IO instead of Guava where possible
Update GitHub Actions to use JDK 14 and JDK 15-ea
For some reason when using annotationProcessorPaths IntelliJ includes the provided and test scoped dependencies on the annotation processor paths.
With this change there would be no test dependencies that IntelliJ can add.
Due to a bug in javac (JDK-8229535) for an annotation with Class values, instead of returning a TypeMirror with TypeKind#ERROR the compiler returns the string "<error>". Eclipse doesn't have this problem currently.
Disable one test in GenericsHierarchyTest for Eclipse on Java 8 due to a bug in the Tycho compiler.
Disable freeBuilder integration test for Eclipse since there are some problems in the second round of annotation processing (no ModelElementProcessor(s) are found)
Adapt checkstyle configuration with new changes:
* Move cacheFile to Checker module
* Move LineLength to Checker module
* Use SuppressWithPlainTextCommentFilter
* Do not use maven-processor-plugin and use the maven-compiler-plugin annotationProcessors instead
* Update NoPackageCyclesRule and exclude tests
* Update checkstyle to 8.14 and remove FIleContentsHolder module and move SuppressionCommentFilter to the TreeWalker
* Update assertj to 3.11.1 and replace usage of RuntimeIOException (from AssertJ) with UncheckedIOException (from java 8)
* Add how to import MapStruct into IntelliJ and Eclipse into the readme
* Move classes from mapstruct-common into mapstruct
* Use Java 8 @Repeatable for @Mappings and @ValueMappings in the mapstruct module
* Add relocation for mapstruct-jdk8 to mapstruct
* Use of 1.8 source and target versions from parent POM
* Update documentation to match
* Update versions of some maven plugin crashing build on Java 8
* Drop JDK 6 & 7 support in integration tests
* Remove mapstruct-common module (it was never deployed to Central)
* Don't run the ProtobufBuilderTest with the processor_plugin_java8 and eclipse_jdt_java_8 (processor plugin runs before the proto java classes are created and the eclipse plugin has some bug)
* Include *.proto for license checks
