JVM IR: extract lowerings to a separate module

Together with extracting codegen to a separate (unrelated) module in the
future, hopefully it'll speed up the build of JVM IR by making it more
parallel, and helping incremental compilation to avoid recompiling code
that depends on lowerings because of `implementation` dependency.

compiler/cli/build.gradle.kts

@@ -12,6 +12,7 @@ dependencies {
     compile(project(":compiler:backend-common"))
     compile(project(":compiler:backend"))
     compile(project(":compiler:backend.jvm"))
+    implementation(project(":compiler:backend.jvm.lower"))
     implementation(project(":compiler:backend.jvm:backend.jvm.entrypoint"))
     compile(project(":compiler:ir.backend.common"))
     compile(project(":compiler:light-classes"))