Fix some dead links in scaladoc

build.sbt

@@ -226,13 +226,17 @@ lazy val unixdomainsocket = alpakkaProject(
 lazy val xml = alpakkaProject("xml", "xml", Dependencies.Xml)
 
 lazy val docs = project
-  .enablePlugins(AkkaParadoxPlugin, ParadoxSitePlugin)
+  .enablePlugins(AkkaParadoxPlugin, ParadoxSitePlugin, PreprocessPlugin)
   .disablePlugins(BintrayPlugin, MimaPlugin)
-  .settings(addMappingsToSiteDir(LocalRootProject / ScalaUnidoc / packageDoc / mappings, SiteScaladoc / siteSubdirName))
   .settings(
     name := "Alpakka",
     publish / skip := true,
-    SiteScaladoc / siteSubdirName := s"api/alpakka/${version.value}",
+    makeSite := makeSite.dependsOn(LocalRootProject / ScalaUnidoc / doc).value,
+    Preprocess / siteSubdirName := s"api/alpakka/${version.value}",
+    Preprocess / sourceDirectory := (LocalRootProject / ScalaUnidoc / unidoc / target).value,
+    Preprocess / preprocessRules := Seq(
+      ("\\.java\\.scala".r, _ => ".java")
+    ),
     Paradox / siteSubdirName := s"docs/alpakka/${version.value}",
     Paradox / sourceDirectory := sourceDirectory.value / "main" / "paradox",
     Paradox / paradoxProperties ++= Map(

project/plugins.sbt

@@ -10,11 +10,11 @@ addSbtPlugin("com.thoughtworks.sbt-api-mappings" % "sbt-api-mappings" % "2.1.0")
 addSbtPlugin("org.foundweekends" % "sbt-bintray" % "0.5.4")
 addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "0.3.0")
 addSbtPlugin("com.lightbend" % "sbt-whitesource" % "0.1.13")
-addSbtPlugin("com.typesafe.sbt" % "sbt-site" % "1.3.2")
+addSbtPlugin("com.typesafe.sbt" % "sbt-site" % "1.3.3-2m")
 addSbtPlugin("com.eed3si9n" % "sbt-unidoc" % "0.4.2")
 addSbtPlugin("com.lightbend.sbt" % "sbt-java-formatter" % "0.4.1")
 addSbtPlugin("com.lightbend.akka.grpc" % "sbt-akka-grpc" % "0.4")
 addSbtPlugin("com.lightbend.sbt" % "sbt-javaagent" % "0.1.4")
 addSbtPlugin("pl.project13.scala" % "sbt-jmh" % "0.3.4")
-// patched version of sbt-dependency-graph
+// patched version of sbt-dependency-graph and sbt-site
 resolvers += Resolver.bintrayIvyRepo("2m", "sbt-plugins")