Bring back cross-platform compat for rootCause

Revert "Make rootCause cross-platform without shims"
This reverts commit 106fe8b.
And commit 038e96b.

munit/js/src/main/scala/munit/internal/InvocationTargetException.scala

@@ -0,0 +1,3 @@
+package munit.internal
+
+class InvocationTargetException extends java.lang.RuntimeException

munit/js/src/main/scala/munit/internal/PlatformCompat.scala

@@ -75,4 +75,8 @@ object PlatformCompat {
   private var myClassLoader: ClassLoader = _
   def setThisClassLoader(loader: ClassLoader): Unit = myClassLoader = loader
   def getThisClassLoader: ClassLoader = myClassLoader
+
+  type InvocationTargetException = munit.internal.InvocationTargetException
+  type UndeclaredThrowableException =
+    munit.internal.UndeclaredThrowableException
 }

munit/js/src/main/scala/munit/internal/UndeclaredThrowableException.scala

@@ -0,0 +1,3 @@
+package munit.internal
+
+class UndeclaredThrowableException extends java.lang.RuntimeException

munit/jvm/src/main/scala/munit/internal/PlatformCompat.scala

@@ -69,4 +69,8 @@ object PlatformCompat {
   def isJS: Boolean = false
   def isNative: Boolean = false
   def getThisClassLoader: ClassLoader = this.getClass().getClassLoader()
+
+  type InvocationTargetException = java.lang.reflect.InvocationTargetException
+  type UndeclaredThrowableException =
+    java.lang.reflect.UndeclaredThrowableException
 }

munit/native/src/main/scala/munit/internal/PlatformCompat.scala

@@ -56,4 +56,8 @@ object PlatformCompat {
   private var myClassLoader: ClassLoader = _
   def setThisClassLoader(loader: ClassLoader): Unit = myClassLoader = loader
   def getThisClassLoader: ClassLoader = myClassLoader
+
+  type InvocationTargetException = java.lang.reflect.InvocationTargetException
+  type UndeclaredThrowableException =
+    java.lang.reflect.UndeclaredThrowableException
 }

munit/shared/src/main/scala/munit/Exceptions.scala

@@ -1,5 +1,8 @@
 package munit
 
+import munit.internal.PlatformCompat.InvocationTargetException
+import munit.internal.PlatformCompat.UndeclaredThrowableException
+
 import java.util.concurrent.ExecutionException
 import scala.annotation.tailrec
 
@@ -9,7 +12,8 @@ object Exceptions {
   // these exception in order to provide more helpful error messages.
   @tailrec
   def rootCause(x: Throwable): Throwable = x match {
-    case _: ExceptionInInitializerError | _: ExecutionException
+    case _: InvocationTargetException | _: ExceptionInInitializerError |
+        _: UndeclaredThrowableException | _: ExecutionException
         if x.getCause != null =>
       rootCause(x.getCause)
     case _ => x