IR: add IrClass.getInlineClassRepresentation, serialize/deserialize it

The change in FirDeclarationUtil is needed because in case of unsigned
types loaded from the standard library, the primary constructor for some
reason is not the first, but the second in the list of constructors.

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/ConversionUtils.kt

@@ -8,6 +8,7 @@ package org.jetbrains.kotlin.fir.backend
 import com.intellij.psi.PsiCompiledElement
 import org.jetbrains.kotlin.KtNodeTypes
 import org.jetbrains.kotlin.descriptors.ClassKind
+import org.jetbrains.kotlin.descriptors.InlineClassRepresentation
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.fir.*
@@ -497,3 +498,14 @@ fun Fir2IrComponents.createTemporaryVariableForSafeCallConstruction(
     conversionScope: Fir2IrConversionScope
 ): Pair<IrVariable, IrValueSymbol> =
     createTemporaryVariable(receiverExpression, conversionScope, "safe_receiver")
+
+// TODO: implement inlineClassRepresentation in FirRegularClass instead.
+fun Fir2IrComponents.computeInlineClassRepresentation(klass: FirRegularClass): InlineClassRepresentation<IrSimpleType>? {
+    if (!klass.isInline) return null
+    val parameter = klass.getInlineClassUnderlyingParameter() ?: error("Inline class has no underlying parameter: ${klass.render()}")
+    val underlyingType = parameter.returnTypeRef.toIrType(typeConverter)
+    return InlineClassRepresentation(
+        parameter.name,
+        underlyingType as? IrSimpleType ?: error("Inline class underlying type is not a simple type: ${klass.render()}")
+    )
+}

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrClassifierStorage.kt

@@ -127,6 +127,10 @@ class Fir2IrClassifierStorage(
         superTypes = klass.superTypeRefs.map { superTypeRef -> superTypeRef.toIrType() }
     }
 
+    private fun IrClass.declareInlineClassRepresentation(klass: FirRegularClass) {
+        inlineClassRepresentation = computeInlineClassRepresentation(klass)
+    }
+
     private fun IrClass.declareSupertypesAndTypeParameters(klass: FirClass<*>): IrClass {
         declareTypeParameters(klass)
         declareSupertypes(klass)
@@ -175,6 +179,7 @@ class Fir2IrClassifierStorage(
         irClass.declareTypeParameters(regularClass)
         irClass.setThisReceiver(regularClass.typeParameters)
         irClass.declareSupertypes(regularClass)
+        irClass.declareInlineClassRepresentation(regularClass)
         return irClass
     }
 

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazyClass.kt

@@ -7,6 +7,7 @@ package org.jetbrains.kotlin.fir.lazy
 
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.fir.backend.Fir2IrComponents
+import org.jetbrains.kotlin.fir.backend.computeInlineClassRepresentation
 import org.jetbrains.kotlin.fir.backend.declareThisReceiverParameter
 import org.jetbrains.kotlin.fir.backend.toIrType
 import org.jetbrains.kotlin.fir.declarations.*
@@ -21,6 +22,7 @@ import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.declarations.lazy.lazyVar
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
+import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.impl.IrSimpleTypeImpl
 import org.jetbrains.kotlin.ir.util.isFakeOverride
@@ -117,6 +119,12 @@ class Fir2IrLazyClass(
         receiver
     }
 
+    override var inlineClassRepresentation: InlineClassRepresentation<IrSimpleType>?
+        get() = computeInlineClassRepresentation(fir)
+        set(_) {
+            error("Mutating Fir2Ir lazy elements is not possible")
+        }
+
     private val fakeOverridesByName = mutableMapOf<Name, Collection<IrDeclaration>>()
 
     fun getFakeOverridesByName(name: Name): Collection<IrDeclaration> = fakeOverridesByName.getOrPut(name) {