[FIR] Remove FirNamedArgumentExpressions during completion

They are mostly necessary for argument mapping during resolution.
To support a couple checkers, we transform named args for varargs
into "fake" spread expressions.

Other than that, named arguments aren't needed for anything and often
lead to bugs where we forget to unwrap them for something, so it's
better to get rid of them.

#KT-66124

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/expressions/FirSpreadArgumentExpression.kt

@@ -24,6 +24,8 @@ abstract class FirSpreadArgumentExpression : FirWrappedArgumentExpression() {
     abstract override val annotations: List<FirAnnotation>
     abstract override val expression: FirExpression
     abstract override val isSpread: Boolean
+    abstract val isNamed: Boolean
+    abstract val isFakeSpread: Boolean
 
     override fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R =
         visitor.visitSpreadArgumentExpression(this, data)

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/expressions/builder/FirSpreadArgumentExpressionBuilder.kt

@@ -26,12 +26,16 @@ class FirSpreadArgumentExpressionBuilder : FirAnnotationContainerBuilder, FirExp
     override var source: KtSourceElement? = null
     override val annotations: MutableList<FirAnnotation> = mutableListOf()
     lateinit var expression: FirExpression
+    var isNamed: Boolean = false
+    var isFakeSpread: Boolean = false
 
     override fun build(): FirSpreadArgumentExpression {
         return FirSpreadArgumentExpressionImpl(
             source,
             annotations.toMutableOrEmpty(),
             expression,
+            isNamed,
+            isFakeSpread,
         )
     }
 

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/expressions/impl/FirSpreadArgumentExpressionImpl.kt

@@ -26,6 +26,8 @@ internal class FirSpreadArgumentExpressionImpl(
     override val source: KtSourceElement?,
     override var annotations: MutableOrEmptyList<FirAnnotation>,
     override var expression: FirExpression,
+    override val isNamed: Boolean,
+    override val isFakeSpread: Boolean,
 ) : FirSpreadArgumentExpression() {
     @OptIn(UnresolvedExpressionTypeAccess::class)
     override val coneTypeOrNull: ConeKotlinType?