Compiler plugin: fix IrLinkageError with K/Js on Kotlin 1.9

Fixes #3556 – IrLinkageError if objects or abstract subclasses of
AbstractProjectConfig exist in K/Js sources

This commit makes the Kotest compiler plugin skip non-instantiable
classes and objects, which derive from AbstractProjectConfig.

Note: To use objects deriving from AbstractProjectConfig on K/Js, they
must be referenced at least once in code that executes, otherwise they
will be discarded (with the IDE warning "object ... is never used)".

kotest-framework/kotest-framework-multiplatform-plugin-embeddable-compiler/src/jvmMain/kotlin/io/kotest/framework/multiplatform/embeddablecompiler/Transformer.kt

@@ -31,7 +31,7 @@ abstract class Transformer(
 
    override fun visitClassNew(declaration: IrClass): IrStatement {
       super.visitClassNew(declaration)
-      if (declaration.isProjectConfig()) configs.add(declaration)
+      if (declaration.isInstantiableProjectConfig()) configs.add(declaration)
       return declaration
    }
 

kotest-framework/kotest-framework-multiplatform-plugin-embeddable-compiler/src/jvmMain/kotlin/io/kotest/framework/multiplatform/embeddablecompiler/specs.kt

@@ -1,5 +1,7 @@
 package io.kotest.framework.multiplatform.embeddablecompiler
 
+import org.jetbrains.kotlin.descriptors.Modality
+import org.jetbrains.kotlin.descriptors.isClass
 import org.jetbrains.kotlin.ir.declarations.IrClass
 import org.jetbrains.kotlin.ir.declarations.IrFile
 import org.jetbrains.kotlin.ir.types.IrType
@@ -27,9 +29,11 @@ val abstractProjectConfigFqName = FqName("io.kotest.core.config.AbstractProjectC
 fun IrFile.specs() = declarations.filterIsInstance<IrClass>().filter { it.isSpecClass() }
 
 /**
- * Returns true if this IrClass is a project config
+ * Returns true if this IrClass is an instantiable project config
  */
-fun IrClass.isProjectConfig() = superTypes().any { it.classFqName == abstractProjectConfigFqName }
+fun IrClass.isInstantiableProjectConfig() =
+   kind.isClass && modality != Modality.ABSTRACT && modality != Modality.SEALED &&
+      superTypes().any { it.classFqName == abstractProjectConfigFqName }
 
 /**
  * Recursively returns all supertypes for an [IrClass] to the top of the type tree.