Support "-language-version" CLI option for compatibility with older releases

Introduce LanguageFeatureSettings, instance of which should be injected by the
container and be accessible everywhere during the compilation (front-end and
back-end).

Parameters of LanguageFeatureSettings are unused in this commit, will be used
later

compiler/testData/cli/js/jsHelp.out

@@ -10,6 +10,7 @@ where possible options include:
   -main {call,noCall}        Whether a main function should be called; default 'call' (main function will be auto detected)
   -output-prefix <path>      Path to file which will be added to the beginning of output file
   -output-postfix <path>     Path to file which will be added to the end of output file
+  -language-version <version> Provide source compatibility with specified language version
   -nowarn                    Generate no warnings
   -verbose                   Enable verbose logging output
   -version                   Display compiler version