Introduce infrastructure to separate string table from metadata on JVM

Nothing especially helpful happens here, this is only a big refactoring
introducing a separate string array for the string table, which is currently
always empty, but will contain actual strings soon

compiler/frontend.java/src/org/jetbrains/kotlin/load/kotlin/incremental/IncrementalPackageFragmentProvider.kt

@@ -117,17 +117,20 @@ public class IncrementalPackageFragmentProvider(
                             allParts.filterNot { it in obsoletePackageParts }
                         } ?: emptyList<String>()
 
-                val dataOfPackageParts = actualPackagePartFiles.map { incrementalCache.getPackagePartData(it) }.filterNotNull()
+                val scopes = actualPackagePartFiles
+                        .map {
+                            incrementalCache.getPackagePartData(it)
+                        }
+                        .filterNotNull()
+                        .map {
+                            IncrementalPackageScope(JvmProtoBufUtil.readPackageDataFrom(it.data, it.strings))
+                        }
 
-                if (dataOfPackageParts.isEmpty()) {
+                if (scopes.isEmpty()) {
                     JetScope.Empty
                 }
                 else {
-                    val scopes = dataOfPackageParts.map { IncrementalPackageScope(JvmProtoBufUtil.readPackageDataFrom(it)) }
-                    ChainedScope(this,
-                                 "Member scope for incremental compilation: union of package parts data",
-                                 *scopes.toTypedArray<JetScope>()
-                    )
+                    ChainedScope(this, "Member scope for incremental compilation: union of package parts data", *scopes.toTypedArray())
                 }
             }
         }

compiler/frontend.java/src/org/jetbrains/kotlin/load/kotlin/incremental/components/IncrementalCache.kt

@@ -16,10 +16,14 @@
 
 package org.jetbrains.kotlin.load.kotlin.incremental.components
 
+import java.io.Serializable
+
+data class JvmPackagePartProto(val data: ByteArray, val strings: Array<String>) : Serializable
+
 public interface IncrementalCache {
     public fun getObsoletePackageParts(): Collection<String>
 
-    public fun getPackagePartData(fqName: String): ByteArray?
+    public fun getPackagePartData(fqName: String): JvmPackagePartProto?
 
     public fun getModuleMappingData(): ByteArray?