Support -experimental/--experimental and -explain/ --explain compiler flags without -O

Author: Gedochao

modules/cli/src/main/scala/scala/cli/commands/shared/ScalacOptions.scala

@@ -64,6 +64,8 @@ object ScalacOptions {
     )
   private val scalacNoArgAliasedOptions = // these options don't require being passed after -O and don't accept an arg
     Set(
+      "experimental",
+      "explain",
       "unchecked",
       "nowarn",
       "feature",

modules/integration/src/test/scala/scala/cli/integration/RunScalacCompatTestDefinitions.scala

@@ -597,10 +597,9 @@ trait RunScalacCompatTestDefinitions {
           TestUtil.cli,
           "run",
           ".",
-          "-O",
-          "-experimental",
           if (useDirective) Nil else macroSettingOptions,
-          extraOptions
+          extraOptions,
+          "-experimental"
         )
           .call(cwd = root, stderr = os.Pipe)
         expect(r.out.trim() == macroSettings.mkString(", "))