Convert FunctionBase to Kotlin, add type parameter to Lambda

This will make it possible to avoid raw types when inheriting from both
FunctionBase and Function<R>. This change adds a generic type parameter
to FunctionBase and Lambda which is not source-breaking under our policy
because both FunctionBase and Lambda are internal classes (located in
package kotlin.jvm.internal)

libraries/stdlib/coroutines/jvm/src/kotlin/coroutines/jvm/internal/ContinuationImpl.kt

@@ -132,13 +132,11 @@ internal interface SuspendFunction
 @SinceKotlin("1.3")
 // Restricted suspension lambdas inherit from this class
 internal abstract class RestrictedSuspendLambda(
-    private val arity: Int,
+    public override val arity: Int,
     completion: Continuation<Any?>?
-) : RestrictedContinuationImpl(completion), FunctionBase, SuspendFunction {
+) : RestrictedContinuationImpl(completion), FunctionBase<Any?>, SuspendFunction {
     constructor(arity: Int) : this(arity, null)
 
-    public override fun getArity(): Int = arity
-
     public override fun toString(): String =
         if (completion == null)
             Reflection.renderLambdaToString(this) // this is lambda
@@ -149,16 +147,14 @@ internal abstract class RestrictedSuspendLambda(
 @SinceKotlin("1.3")
 // Suspension lambdas inherit from this class
 internal abstract class SuspendLambda(
-    private val arity: Int,
+    public override val arity: Int,
     completion: Continuation<Any?>?
-) : ContinuationImpl(completion), FunctionBase, SuspendFunction {
+) : ContinuationImpl(completion), FunctionBase<Any?>, SuspendFunction {
     constructor(arity: Int) : this(arity, null)
 
-    public override fun getArity(): Int = arity
-
     public override fun toString(): String =
         if (completion == null)
             Reflection.renderLambdaToString(this) // this is lambda
         else
             super.toString() // this is continuation
-}
+}