[JS] Extract sourcemap generating related files to a separate module

It's required to reuse the same infrastructure in the new backend.

compiler/cli/cli-js/build.gradle.kts

@@ -17,6 +17,7 @@ dependencies {
     compile(project(":js:js.translator"))
     compile(project(":js:js.serializer"))
     compile(project(":js:js.dce"))
+    compile(project(":js:js.sourcemap"))
 
     compileOnly(intellijCoreDep()) { includeJars("intellij-core") }
 }