Compile kotlin-runtime-minimal.jar, run proguard against it

ProGuard complains if we're trying to shrink compiler with the full runtime in
dependencies because for the compiler produced on the first step of bootstrap
these two jars contain conflicting classes. This won't matter in the final
distribution because we will strip 'core' modules from compiler.jar. But this
matters in the first step because core will be different in the compiler (used
to load compiled class files) and in the reflection (used to introspect symbols
at runtime).

kotlin-runtime-minimal.jar still contains the complete reflection API and some
stub implementations in module 'reflection.stub.jvm', but doesn't have core, so
it won't cause a proguard error
Rework bootstrapping compiler with runtime in build.xml

Do not pack the runtime into the compiler on the first step of bootstrap, but
rather leave it as a separate file named kotlin-runtime-internal-bootstrap.jar.

This new solution will allow compiler to use its own classes from "core", not
the ones used by the runtime it depends on
Refactor CompilerRunnerUtil

Eliminate code duplication, add NotNull, make everything private, etc
Move ParentLastURLClassLoader from gradle plugin to compiler
Use parent-last class loader in IDE compiler runner

To be able to invoke the intermediate compiler built on the first step of
bootstrap: in contrast to the distributed compiler, it's incompatible with the
runtime produced by itself and should instead be run with the runtime in the
classpath which was used to compile it
Minor, rename module to conform to naming style
Include different runtime into plugin for bootstrap build