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/reflect/api/build.gradle

@@ -0,0 +1,32 @@
+description = ''
+
+apply plugin: 'kotlin'
+
+configureJvm6Project(project)
+
+sourceSets {
+    main {
+        java {
+            srcDir "${rootDir}/core/reflection.jvm/src"
+        }
+    }
+}
+
+dependencies {
+    compileOnly project(':kotlin-stdlib')
+    compileOnly project(':core:descriptors')
+    compileOnly project(':core:descriptors.jvm')
+    compileOnly project(':core:deserialization')
+    compileOnly project(':core:descriptors.runtime')
+    compileOnly project(':core:util.runtime')
+}
+
+compileKotlin {
+    kotlinOptions {
+        freeCompilerArgs = ["-version",
+                            "-Xallow-kotlin-package",
+                            "-Xnormalize-constructor-calls=enable",
+                            "-module-name", "kotlin-reflection",
+                            "-Xdump-declarations-to=${buildDir}/reflect-declarations.json"]
+    }
+}