[JS IR] Build stdlib using compiler from repo

Previously JS IR versions of stdlib and kotlin-test were build
by default using compiler previously built on a buildserver.

It had some issues:
 - This required us to advance bootstrap every time we made any
   incompatible IR changes. This happens often since IR ABI is
   not quite stable yet.

 - We never tested the exact combination of compiler and stdlib we publish

   We tested:
    - new compiler with new stdlib build by new compiler (in box tests)
    - old compiler with new stdlib build by old compiler (in stdlib tests)

   We published:
    - new compiler with new stdlib build by old compiler

After this change JS IR compiler tests, builds and publishes
single configuration:

    new compiler with new stdlib build by new compiler

JS IR stdlib and kotlin-test are now built using JavaExec of CLI instead
of Gradle plugin to avoid troubles of loading a freshly built plugin.

This also allows to have a granular dependencies: we don't rebuild klib
if we changed a lowering in a compiler backend, but we do rebuild it if
we changed IR serialization algorithm.

compiler/tests/org/jetbrains/kotlin/code/CodeConformanceTest.kt

@@ -93,7 +93,7 @@ class CodeConformanceTest : TestCase() {
             "libraries/tools/kotlin-source-map-loader/.gradle",
             "libraries/tools/kotlin-source-map-loader/lib",
             "buildSrc/prepare-deps/build",
-            "compiler/ir/serialization.js/build"
+            "libraries/stdlib/js-ir/build/"
         )
     }