Migrate functional tests to Kotlin and Junit part 5 (#1134)

* Rename containsEntries and assertDoesNotContain

* Add BaseCachingTest

* Convert MinimizationCachingSpec

* Convert RelocationCachingSpec

* Rename ConfigurationCacheSpec

* Convert ShadowJarCachingSpec

* Clean up TransformCachingSpec

* Convert TransformCachingSpec

* Remove AbstractCachingSpec

* Replace transform blocks

* Cleanups

* Reuse writeMainClass

* Move transform kit to BasePluginTest

* Ruse runner and run

* Try to cache JarPath

* Revert "Try to cache JarPath"

This reverts commit 19dfd90.

* Close reader in getContent

* Unify task paths

* Unify runner function

* Fix shadowJarIsCachedCorrectlyWhenOutputFileIsChanged

* Remove BasePluginSpecification

Author: Goooler