Scripting: refactor plugin command line processing

- process command line properly when plugin is autoloaded
- add and fix options to disable definitions autoloading and discovery
- cleanup unused code
(partial test is added to "avoid definitions discovery" commit)

plugins/scripting/scripting-compiler-impl/src/org/jetbrains/kotlin/scripting/configuration/ScriptingConfigurationKeys.kt

@@ -29,6 +29,9 @@ object ScriptingConfigurationKeys {
     val DISABLE_SCRIPT_DEFINITIONS_FROM_CLASSPATH_OPTION: CompilerConfigurationKey<Boolean> =
         CompilerConfigurationKey.create("Do not extract script definitions from the compilation classpath")
 
+    val DISABLE_SCRIPT_DEFINITIONS_AUTOLOADING_OPTION: CompilerConfigurationKey<Boolean> =
+        CompilerConfigurationKey.create("Do not automatically load compiler-supplied script definitions, like main-kts")
+
     val LEGACY_SCRIPT_RESOLVER_ENVIRONMENT_OPTION: CompilerConfigurationKey<MutableMap<String, Any?>> =
         CompilerConfigurationKey.create("Script resolver environment")
 }