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

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

js/js.translator/build.gradle.kts

@@ -14,6 +14,7 @@ dependencies {
     compile(project(":js:js.ast"))
     compile(project(":js:js.frontend"))
     compile(project(":js:js.parser"))
+    compileOnly(project(":js:js.sourcemap"))
     compileOnly(intellijCoreDep()) { includeJars("intellij-core") }
     compileOnly(intellijDep()) { includeJars("trove4j", "guava", rootProject = rootProject) }
 }
@@ -30,4 +31,4 @@ configure<IdeaModel> {
     module {
         excludeDirs = excludeDirs + files("testData/out", "testData/out-min")
     }
-}
+}