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/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/CommonCompilerArguments.java

@@ -25,6 +25,10 @@ import java.util.List;
 public abstract class CommonCompilerArguments {
     public static final String PLUGIN_OPTION_FORMAT = "plugin:<pluginId>:<optionName>=<value>";
 
+    @Argument(value = "language-version", description = "Provide source compatibility with specified language version")
+    @ValueDescription("<version>")
+    public String languageVersion;
+
     @Argument(value = "nowarn", description = "Generate no warnings")
     public boolean suppressWarnings;