Build: implement useBootstrapStdlib flag

Excludes stdlib projects from build and uses bootstrap stdlib artifacts

 #KT-29205

libraries/reflect/api/build.gradle

@@ -14,7 +14,7 @@ sourceSets {
 }
 
 dependencies {
-    compile project(':kotlin-stdlib')
+    compile kotlinStdlib()
     compileOnly project(':core:descriptors')
     compileOnly project(':core:descriptors.jvm')
     compileOnly project(':core:deserialization')

libraries/reflect/build.gradle.kts

@@ -47,9 +47,9 @@ configurations.getByName("compileOnly").extendsFrom(shadows)
 val mainJar by configurations.creating
 
 dependencies {
-    compile(project(":kotlin-stdlib"))
+    compile(kotlinStdlib())
 
-    proguardDeps(project(":kotlin-stdlib"))
+    proguardDeps(kotlinStdlib())
     proguardAdditionalInJars(project(":kotlin-annotations-jvm"))
     proguardDeps(files(firstFromJavaHomeThatExists("jre/lib/rt.jar", "../Classes/classes.jar", jdkHome = File(property("JDK_16") as String))))