[FIR] Use ConeKotlinType to represent vararg's element type

We are using `ConeKotlinType` instead of `FirTypeRef` to represent
that element type of vararg doesn't have any source. It has a type
that was inferred. If we try to specify a source, then we could
end up with the incorrect place for diagnostic.

#KT-59682 Fixed

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

@@ -11,7 +11,6 @@ package org.jetbrains.kotlin.fir.expressions
 import org.jetbrains.kotlin.KtSourceElement
 import org.jetbrains.kotlin.fir.FirElement
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
-import org.jetbrains.kotlin.fir.types.FirTypeRef
 import org.jetbrains.kotlin.fir.visitors.FirTransformer
 import org.jetbrains.kotlin.fir.visitors.FirVisitor
 
@@ -24,7 +23,7 @@ abstract class FirVarargArgumentsExpression : FirExpression() {
     abstract override val coneTypeOrNull: ConeKotlinType?
     abstract override val annotations: List<FirAnnotation>
     abstract val arguments: List<FirExpression>
-    abstract val varargElementType: FirTypeRef
+    abstract val coneElementTypeOrNull: ConeKotlinType?
 
     override fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R =
         visitor.visitVarargArgumentsExpression(this, data)

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

@@ -20,7 +20,6 @@ import org.jetbrains.kotlin.fir.expressions.FirExpression
 import org.jetbrains.kotlin.fir.expressions.FirVarargArgumentsExpression
 import org.jetbrains.kotlin.fir.expressions.impl.FirVarargArgumentsExpressionImpl
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
-import org.jetbrains.kotlin.fir.types.FirTypeRef
 
 @FirBuilderDsl
 class FirVarargArgumentsExpressionBuilder : FirAnnotationContainerBuilder, FirExpressionBuilder {
@@ -28,7 +27,7 @@ class FirVarargArgumentsExpressionBuilder : FirAnnotationContainerBuilder, FirEx
     override var coneTypeOrNull: ConeKotlinType? = null
     override val annotations: MutableList<FirAnnotation> = mutableListOf()
     val arguments: MutableList<FirExpression> = mutableListOf()
-    lateinit var varargElementType: FirTypeRef
+    var coneElementTypeOrNull: ConeKotlinType? = null
 
     override fun build(): FirVarargArgumentsExpression {
         return FirVarargArgumentsExpressionImpl(
@@ -36,14 +35,14 @@ class FirVarargArgumentsExpressionBuilder : FirAnnotationContainerBuilder, FirEx
             coneTypeOrNull,
             annotations.toMutableOrEmpty(),
             arguments,
-            varargElementType,
+            coneElementTypeOrNull,
         )
     }
 
 }
 
 @OptIn(ExperimentalContracts::class)
-inline fun buildVarargArgumentsExpression(init: FirVarargArgumentsExpressionBuilder.() -> Unit): FirVarargArgumentsExpression {
+inline fun buildVarargArgumentsExpression(init: FirVarargArgumentsExpressionBuilder.() -> Unit = {}): FirVarargArgumentsExpression {
     contract {
         callsInPlace(init, InvocationKind.EXACTLY_ONCE)
     }

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

@@ -18,7 +18,6 @@ import org.jetbrains.kotlin.fir.expressions.FirExpression
 import org.jetbrains.kotlin.fir.expressions.FirVarargArgumentsExpression
 import org.jetbrains.kotlin.fir.expressions.UnresolvedExpressionTypeAccess
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
-import org.jetbrains.kotlin.fir.types.FirTypeRef
 import org.jetbrains.kotlin.fir.visitors.FirTransformer
 import org.jetbrains.kotlin.fir.visitors.FirVisitor
 import org.jetbrains.kotlin.fir.visitors.transformInplace
@@ -30,19 +29,17 @@ internal class FirVarargArgumentsExpressionImpl(
     override var coneTypeOrNull: ConeKotlinType?,
     override var annotations: MutableOrEmptyList<FirAnnotation>,
     override val arguments: MutableList<FirExpression>,
-    override var varargElementType: FirTypeRef,
+    override val coneElementTypeOrNull: ConeKotlinType?,
 ) : FirVarargArgumentsExpression() {
 
     override fun <R, D> acceptChildren(visitor: FirVisitor<R, D>, data: D) {
         annotations.forEach { it.accept(visitor, data) }
         arguments.forEach { it.accept(visitor, data) }
-        varargElementType.accept(visitor, data)
     }
 
     override fun <D> transformChildren(transformer: FirTransformer<D>, data: D): FirVarargArgumentsExpressionImpl {
         transformAnnotations(transformer, data)
         arguments.transformInplace(transformer, data)
-        varargElementType = varargElementType.transform(transformer, data)
         return this
     }