[FIR] Add isFoldedString property to FirStringConcatenationCall

FirStringConcatenationCall can represent two language constructs:
1. String interpolation
2. String literals concatenations

The latter one is identified by isFoldedString property.

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

@@ -326,6 +326,7 @@ class LightTreeRawFirExpressionBuilder(
             argumentList = buildArgumentList { arguments += output.asReversed().map { getAsFirExpression<FirExpression>(it) } }
             source = binaryExpression.toFirSourceElement()
             interpolationPrefix = ""
+            isFoldedStrings = true
         }
     }
 

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

@@ -24,6 +24,7 @@ abstract class FirStringConcatenationCall : FirExpression(), FirCall {
     @UnresolvedExpressionTypeAccess
     abstract override val coneTypeOrNull: ConeKotlinType?
     abstract val interpolationPrefix: String
+    abstract val isFoldedStrings: Boolean
 
     override fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R =
         visitor.visitStringConcatenationCall(this, data)

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

@@ -27,13 +27,15 @@ class FirStringConcatenationCallBuilder : FirCallBuilder, FirAnnotationContainer
     override val annotations: MutableList<FirAnnotation> = mutableListOf()
     override lateinit var argumentList: FirArgumentList
     lateinit var interpolationPrefix: String
+    var isFoldedStrings: Boolean = false
 
     override fun build(): FirStringConcatenationCall {
         return FirStringConcatenationCallImpl(
             source,
             annotations.toMutableOrEmpty(),
             argumentList,
             interpolationPrefix,
+            isFoldedStrings,
         )
     }
 

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

@@ -30,6 +30,7 @@ internal class FirStringConcatenationCallImpl(
     override var annotations: MutableOrEmptyList<FirAnnotation>,
     override var argumentList: FirArgumentList,
     override val interpolationPrefix: String,
+    override val isFoldedStrings: Boolean,
 ) : FirStringConcatenationCall() {
     @OptIn(UnresolvedExpressionTypeAccess::class)
     override val coneTypeOrNull: ConeKotlinType? = StandardClassIds.String.constructClassLikeType()

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/BuilderConfigurator.kt

@@ -279,6 +279,7 @@ class BuilderConfigurator(model: Model) : AbstractFirBuilderConfigurator<Abstrac
 
         builder(stringConcatenationCall) {
             parents += callBuilder
+            defaultFalse("isFoldedStrings")
         }
 
         builder(thisReceiverExpression) {

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/FirTree.kt

@@ -1014,6 +1014,7 @@ object FirTree : AbstractFirTreeBuilder() {
         parent(expression)
 
         +field("interpolationPrefix", string)
+        +field("isFoldedStrings", boolean)
     }
 
     val throwExpression: Element by element(Expression) {