Build: implement useBootstrapStdlib flag

Excludes stdlib projects from build and uses bootstrap stdlib artifacts

 #KT-29205

core/descriptors/build.gradle.kts

@@ -8,7 +8,7 @@ javaHome = rootProject.extra["JDK_16"] as String
 
 dependencies {
     compile(project(":core:util.runtime"))
-    compile(project(":kotlin-stdlib"))
+    compile(kotlinStdlib())
     compileOnly("org.jetbrains:annotations:13.0")
     compile(project(":kotlin-annotations-jvm"))
 }