[FIR] Set vararg modifier on data class copy method parameters

This only happens in red code, but it prevents unhelpful initializer
type mismatch errors.

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/stubBased/deserialization/StubBasedClassDeserialization.kt

@@ -212,6 +212,7 @@ internal fun deserializeClassToSymbol(
                     },
                     toFirSource = { src, kind -> KtFakeSourceElement(src as PsiElement, kind) },
                     addValueParameterAnnotations = { annotations += context.annotationDeserializer.loadAnnotations(it) },
+                    isVararg = { it.isVarArg }
                 )
             )
         }

compiler/fir/analysis-tests/testData/resolve/suppress/withSuppression.fir.txt

@@ -31,6 +31,6 @@ FILE: withSuppression.kt
 
         public final operator fun component1(): R|kotlin/String|
 
-        public final fun copy(x: R|kotlin/String| = this@R|/D|.R|/D.x|): R|D|
+        public final fun copy(vararg x: R|kotlin/Array<out kotlin/String>| = this@R|/D|.R|/D.x|): R|D|
 
     }

compiler/fir/raw-fir/light-tree2fir/src/org/jetbrains/kotlin/fir/lightTree/converter/AbstractLightTreeRawFirBuilder.kt

@@ -132,6 +132,9 @@ abstract class AbstractLightTreeRawFirBuilder(
     override val LighterASTNode?.indexExpressions: List<LighterASTNode>?
         get() = this?.getLastChildExpression()?.getChildrenAsArray()?.filterNotNull()?.filter { it.isExpression() }
 
+    override val LighterASTNode.isVararg: Boolean
+        get() = getChildNodeByType(KtNodeTypes.MODIFIER_LIST)?.getChildNodeByType(VARARG_KEYWORD) != null
+
     fun LighterASTNode.getParent(): LighterASTNode? {
         return tree.getParent(this)
     }

compiler/fir/raw-fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/PsiRawFirBuilder.kt

@@ -140,6 +140,9 @@ open class PsiRawFirBuilder(
     override val PsiElement?.indexExpressions: List<PsiElement>?
         get() = (this as? KtArrayAccessExpression)?.indexExpressions
 
+    override val PsiElement.isVararg: Boolean
+        get() = (this as? KtParameter)?.isVarArg ?: false
+
     private val KtModifierListOwner.visibility: Visibility
         get() = with(modifierList) {
             when {

compiler/fir/raw-fir/raw-fir.common/src/org/jetbrains/kotlin/fir/builder/AbstractRawFirBuilder.kt

@@ -63,6 +63,7 @@ abstract class AbstractRawFirBuilder<T>(val baseSession: FirSession, val context
     abstract val T?.selectorExpression: T?
     abstract val T?.arrayExpression: T?
     abstract val T?.indexExpressions: List<T>?
+    abstract val T.isVararg: Boolean
 
     /**** Class name utils ****/
     inline fun <T> withChildClassName(
@@ -901,6 +902,7 @@ abstract class AbstractRawFirBuilder<T>(val baseSession: FirSession, val context
                     createParameterTypeRefWithSourceKind,
                     { src, kind -> src?.toFirSourceElement(kind) },
                     addValueParameterAnnotations,
+                    { it.isVararg },
                 )
             )
         }
@@ -1028,21 +1030,22 @@ abstract class AbstractRawFirBuilder<T>(val baseSession: FirSession, val context
     }
 }
 
-fun <T> FirRegularClassBuilder.createDataClassCopyFunction(
+fun <TBase, TSource : TBase, TParameter : TBase> FirRegularClassBuilder.createDataClassCopyFunction(
     classId: ClassId,
-    sourceElement: T,
+    sourceElement: TSource,
     dispatchReceiver: ConeClassLikeType?,
-    zippedParameters: List<Pair<T, FirProperty>>,
+    zippedParameters: List<Pair<TParameter, FirProperty>>,
     createClassTypeRefWithSourceKind: (KtFakeSourceElementKind) -> FirTypeRef,
     createParameterTypeRefWithSourceKind: (FirProperty, KtFakeSourceElementKind) -> FirTypeRef,
-    toFirSource: (T?, KtFakeSourceElementKind) -> KtSourceElement?,
+    toFirSource: (TBase?, KtFakeSourceElementKind) -> KtSourceElement?,
-    addValueParameterAnnotations: FirValueParameterBuilder.(T) -> Unit,
+    addValueParameterAnnotations: FirValueParameterBuilder.(TParameter) -> Unit,
+    isVararg: (TParameter) -> Boolean,
 ): FirSimpleFunction {
     fun generateComponentAccess(
         parameterSource: KtSourceElement?,
         firProperty: FirProperty,
         classTypeRefWithCorrectSourceKind: FirTypeRef,
-        firPropertyReturnTypeRefWithCorrectSourceKind: FirTypeRef
+        firPropertyReturnTypeRefWithCorrectSourceKind: FirTypeRef,
     ) =
         buildPropertyAccessExpression {
             this.source = parameterSource
@@ -1088,7 +1091,7 @@ fun <T> FirRegularClassBuilder.createDataClassCopyFunction(
                 defaultValue = generateComponentAccess(parameterSource, firProperty, classTypeRef, propertyReturnTypeRef)
                 isCrossinline = false
                 isNoinline = false
-                isVararg = false
+                this.isVararg = isVararg(ktParameter)
                 addValueParameterAnnotations(ktParameter)
                 for (annotation in annotations) {
                     annotation.replaceUseSiteTarget(null)