This allows to get rid of the dependency on descriptors.runtime from
compiler/IDE tests which is problematic: classes there clash with the
classes in kotlin-reflect, which reference declarations in shadowed
packages
To make it obvious that this is a part of kotlin-reflect and should not
be packed into the compiler jar. Also copy 'classId' utility to
AbstractLocalClassProtoTest to minimize dependencies on
kotlin.reflect.jvm.internal
Note that the module itself is still needed and can't be merged into
kotlin-reflect because of the way it's used in
AbstractJvmRuntimeDescriptorLoaderTest
MockLibraryUtil runs the compiler in the new class loader, which is
useful for IDE tests to avoid loading KotlinCoreEnvironment, but is not
needed and is suboptimal for compiler tests.
Also use another method in AbstractForeignAnnotationsTest to assert that
there are no files in the compiled libraries
Mikhail Zarechenskiy