Add support of internal arguments for language feature settings

Arguments are passed in form '-XXLanguage:+LanguageFeatureName' for enabling
LanguageFeature.LanguageFeatureName, and '-XXLanguage:-LanguageFeatureName'
for disabling.

Note that they do override other settings, including 'language-version'
or extra ('-X') args.

compiler/tests-common/tests/org/jetbrains/kotlin/checkers/CompilerTestLanguageVersionSettings.kt

@@ -42,6 +42,8 @@ data class CompilerTestLanguageVersionSettings(
     override fun getFeatureSupport(feature: LanguageFeature): LanguageFeature.State =
             languageFeatures[feature] ?: delegate.getFeatureSupport(feature)
 
+    override fun isPreRelease(): Boolean = languageVersion.isPreRelease()
+
     @Suppress("UNCHECKED_CAST")
     override fun <T> getFlag(flag: AnalysisFlag<T>): T = analysisFlags[flag] as T? ?: flag.defaultValue
 }