Test, scripting: add infra for script tests with customizable def

based on the regular compiler tests infrastructure, but adding
directives that can customize the definition from testdata.
So far only default imports and provided properties are supported, but
the infrastructure is easily extendable to other customizations.
Another limitations that provided properties are not supported for
the black box tests - the constructor parameters computing code
should be adapted to support it.
Note: in order to pick up the customized definition, the script files
should have an extension .test.kts

build.gradle.kts

@@ -832,6 +832,7 @@ tasks {
         dependsOn(":kotlin-scripting-common:test")
         dependsOn(":kotlin-scripting-jvm:test")
         dependsOn(":kotlin-scripting-jvm-host-test:test")
+        dependsOn(":plugins:scripting:scripting-tests:test")
         dependsOn(":kotlin-scripting-dependencies:test")
         dependsOn(":kotlin-scripting-dependencies-maven:test")
         dependsOn(":kotlin-scripting-dependencies-maven-all:test")