Extract kotlin-reflect-api module out of kotlin-reflect

This is needed only for faster compilation of the Kotlin project itself
and has no effect on the public artifact
org.jetbrains.kotlin:kotlin-reflect.

The problem this is solving is the rebuild of the project once anything
has been changed in modules in 'core' (even inside function bodies, i.e.
a non-API change). Previously, changes in 'core' led to the compilation
of kotlin-reflect, which led to the rebuild of all modules depending on
kotlin-reflect directly or indirectly (which is almost all modules in
the project) because kotlin-reflect's artifacts are custom-built and the
changes can not be picked up incrementally. But 99.9% of the time the
initial changes in 'core' could not have any effect on the usages of
kotlin-reflect, because classes from those modules are moved to an
internal package in kotlin-reflect and thus are an internal
implementation detail.

Now, changes in 'core' still lead to the compilation of kotlin-reflect
and to the process of building the custom jar. But if a module depends
on kotlin-reflect-api, not kotlin-reflect, then the incremental
difference checker will detect that the module does not have to be
recompiled if there hasn't been any changes to the API of
kotlin-reflect-api. Which means that the module will not be rebuilt on
every change in 'core'.

This commit only introduces the new module. The dependencies
(kotlin-reflect -> kotlin-reflect-api) are replaced in the next commit.

libraries/commonConfiguration.gradle

@@ -20,6 +20,15 @@ ext.configureJvmProject = { Project project ->
     }
 }
 
+ext.configureJavaOnlyJvm6Project = { Project project ->
+    project.tasks.withType(JavaCompile) {
+        sourceCompatibility = 1.6
+        targetCompatibility = 1.6
+        options.fork = true
+        options.forkOptions.javaHome = file(JDK_16)
+    }
+}
+
 ext.configureJvm6Project = { Project project ->
     project.configure(project) {
         project.ext.jvmTarget = "1.6"
@@ -30,12 +39,7 @@ ext.configureJvm6Project = { Project project ->
             from sourceSets.main.kotlin
         }
 
-        tasks.withType(JavaCompile) {
-            sourceCompatibility = 1.6
-            targetCompatibility = 1.6
-            options.fork = true
-            options.forkOptions.javaHome = file(JDK_16)
-        }
+        configureJavaOnlyJvm6Project(project)
 
         tasks.withType(project.compileKotlin.class) {
             kotlinOptions.jdkHome = JDK_16