fix: fix wrong mill source layout

Trait HasScala2Plugin and HasScala2MacroAnno extending CrossSbtModule
will override the mill sources with SBT's folder layout and it will
break the modules with mill's default source layout like LitUtility
and PanamaConverter.

Signed-off-by: unlsycn <unlsycn@unlsycn.com>

build.sc

@@ -119,15 +119,15 @@ trait ChiselPublishModule extends CiReleaseModule {
 
 }
 
-trait HasScala2MacroAnno extends CrossSbtModule {
+trait HasScala2MacroAnno extends CrossModuleBase {
   override def scalacOptions = T {
     if (!v.isScala3(crossScalaVersion)) {
       super.scalacOptions() ++ Agg("-Ymacro-annotations")
     } else super.scalacOptions()
   }
 }
 
-trait HasScala2Plugin extends CrossSbtModule {
+trait HasScala2Plugin extends CrossModuleBase {
   def pluginModule: Plugin
 
   override def scalacOptions = T {