[Gradle][MPP] Cache kotlinProjectStructureMetadata for multiplatform projects

GranularMetadataTransformation requires the metadata for dependency
projects, for every given source set multiple times. This lead
to the metadata being built extremely often, causing a significant
bottleneck during import.

libraries/tools/kotlin-tooling-metadata/src/main/kotlin/org/jetbrains/kotlin/tooling/KotlinToolingMetadata.kt

@@ -72,5 +72,3 @@ data class KotlinToolingMetadata(
         const val currentSchemaVersion: String = "1.1.0"
     }
 }
-
-