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/testData/cli/jvm/internalArgumentOverrideExtraArgument.out

@@ -0,0 +1,13 @@
+warning: ATTENTION!
+This build uses internal compiler arguments:
+
+-XXLanguage:+SoundSmartCastsAfterTry
+
+This mode is strictly prohibited for production use,
+as no stability/compatibility guarantees are given on
+compiler or generated code. Use it at your own risk!
+
+compiler/testData/cli/jvm/legacySmartCastsAfterTry.kt:8:9: error: only safe (?.) or non-null asserted (!!.) calls are allowed on a nullable receiver of type String?
+    some.length
+        ^
+COMPILATION_ERROR