FIR CFA: add control flow between default parameter values

function enter -> default 1 -> default 2 -> rest of function
                   \----------^ \----------^

This probably has no effect (in non-stupid code, at least), but it makes
graph construction more architecturally correct (now value parameters'
subgraphs get attached to a node).

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/dfa/cfg/CFGNode.kt

@@ -182,8 +182,14 @@ class LocalFunctionDeclarationNode(owner: ControlFlowGraph, override val fir: Fi
 
 // ----------------------------------- Default arguments -----------------------------------
 
+class EnterValueParameterNode(owner: ControlFlowGraph, override val fir: FirValueParameter, level: Int, id: Int) : CFGNodeWithCfgOwner<FirValueParameter>(owner, level, id) {
+    override fun <R, D> accept(visitor: ControlFlowGraphVisitor<R, D>, data: D): R {
+        return visitor.visitEnterValueParameterNode(this, data)
+    }
+}
+
 @OptIn(CfgInternals::class)
-class EnterDefaultArgumentsNode(owner: ControlFlowGraph, override val fir: FirValueParameter, level: Int, id: Int) : CFGNodeWithCfgOwner<FirValueParameter>(owner, level, id),
+class EnterDefaultArgumentsNode(owner: ControlFlowGraph, override val fir: FirValueParameter, level: Int, id: Int) : CFGNode<FirValueParameter>(owner, level, id),
     EnterNodeMarker {
     init {
         owner.enterNode = this
@@ -206,6 +212,12 @@ class ExitDefaultArgumentsNode(owner: ControlFlowGraph, override val fir: FirVal
     }
 }
 
+class ExitValueParameterNode(owner: ControlFlowGraph, override val fir: FirValueParameter, level: Int, id: Int) : CFGNode<FirValueParameter>(owner, level, id) {
+    override fun <R, D> accept(visitor: ControlFlowGraphVisitor<R, D>, data: D): R {
+        return visitor.visitExitValueParameterNode(this, data)
+    }
+}
+
 // ----------------------------------- Anonymous function -----------------------------------
 
 class SplitPostponedLambdasNode(owner: ControlFlowGraph, override val fir: FirStatement, val lambdas: List<FirAnonymousFunction>, level: Int, id: Int)

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/dfa/cfg/CFGNodeRenderer.kt

@@ -115,8 +115,10 @@ fun CFGNode<*>.render(): String =
 
                 is ContractDescriptionEnterNode -> "Enter contract description"
 
+                is EnterValueParameterNode -> "Enter default value of ${fir.name}"
                 is EnterDefaultArgumentsNode -> "Enter default value of ${fir.name}"
                 is ExitDefaultArgumentsNode -> "Exit default value of ${fir.name}"
+                is ExitValueParameterNode -> "Exit default value of ${fir.name}"
 
                 is ElvisLhsExitNode -> "Exit lhs of ?:"
                 is ElvisLhsIsNotNullNode -> "Lhs of ?: is not null"

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/dfa/cfg/ControlFlowGraphVisitor.kt

@@ -26,7 +26,7 @@ abstract class ControlFlowGraphVisitor<out R, in D> {
 
     // ----------------------------------- Default arguments -----------------------------------
 
-    open fun visitExitDefaultArgumentsNode(node: ExitDefaultArgumentsNode, data: D): R {
+    open fun visitEnterValueParameterNode(node: EnterValueParameterNode, data: D): R {
         return visitNode(node, data)
     }
 
@@ -34,6 +34,14 @@ abstract class ControlFlowGraphVisitor<out R, in D> {
         return visitNode(node, data)
     }
 
+    open fun visitExitDefaultArgumentsNode(node: ExitDefaultArgumentsNode, data: D): R {
+        return visitNode(node, data)
+    }
+
+    open fun visitExitValueParameterNode(node: ExitValueParameterNode, data: D): R {
+        return visitNode(node, data)
+    }
+
     // ----------------------------------- Anonymous function -----------------------------------
 
     open fun visitSplitPostponedLambdasNode(node: SplitPostponedLambdasNode, data: D): R {