Rename platform to header.

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/descriptors/IrBuiltinFunctionDescriptor.kt

@@ -54,7 +54,7 @@ abstract class IrBuiltinOperatorDescriptorBase(containingDeclaration: Declaratio
     override fun isOperator(): Boolean = false
     override fun isSuspend(): Boolean = false
     override fun isTailrec(): Boolean = false
-    override fun isPlatform(): Boolean = false
+    override fun isHeader(): Boolean = false
     override fun isImpl(): Boolean = false
     override fun hasStableParameterNames(): Boolean = true
     override fun hasSynthesizedParameterNames(): Boolean = false

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/descriptors/IrDelegateDescriptor.kt

@@ -60,7 +60,7 @@ abstract class IrDelegateDescriptorBase(
         SourceElement.NO_SOURCE,
         /* lateInit = */ false,
         /* isConst = */ false,
-        /* isPlatform = */ false,
+        /* isHeader = */ false,
         /* isImpl = */ false,
         /* isExternal = */ false
 ) {