Add platform/impl soft keywords, add isPlatform/isImpl to MemberDescriptor

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

@@ -54,6 +54,8 @@ 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 isImpl(): Boolean = false
     override fun hasStableParameterNames(): Boolean = true
     override fun hasSynthesizedParameterNames(): Boolean = false