[LL FIR] implement diagnostic tests on custom script definitions

it is impossible to declare test data with another output yet
as `myScriptFile.test.ll.kts` won't be treated as custom definition as
it requires `test.kts` extension.

^KT-66232 Fixed
^KT-66276

plugins/scripting/scripting-tests/test/org/jetbrains/kotlin/scripting/test/AbstractScriptTestBaseClasses.kt

@@ -30,7 +30,7 @@ open class AbstractScriptWithCustomDefBlackBoxCodegenTest : AbstractFirScriptCod
     }
 }
 
-private fun TestConfigurationBuilder.configureWithCustomScriptDef() {
+fun TestConfigurationBuilder.configureWithCustomScriptDef() {
     useConfigurators(
         ::ScriptWithCustomDefEnvironmentConfigurator
     )

plugins/scripting/scripting-tests/testData/diagnostics/testScripts/providedProperties.test.kts

@@ -1,3 +1,4 @@
 // SCRIPT_PROVIDED_PROPERTIES: prop1: kotlin.String, prop2: java.io.File
+// MUTE_LL_FIR: KT-66276
 
 val rv = args[1] + prop1 + prop2.path

plugins/scripting/scripting-tests/testData/diagnostics/testScripts/providedPropertiesShadowing.test.kts

@@ -1,4 +1,5 @@
 // SCRIPT_PROVIDED_PROPERTIES: prop1: kotlin.String
+// MUTE_LL_FIR: KT-66276
 
 val prop1 = 42 // TODO: Error should be reported on this shadowing, see KT-65809