Explicit Api mode: prototype with check for missing explicit visibility

Add cli flag with 3-state switch

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/CommonCompilerArguments.kt

@@ -316,6 +316,14 @@ abstract class CommonCompilerArguments : CommonToolArguments() {
     @Argument(value = "-Xdisable-default-scripting-plugin", description = "Do not enable scripting plugin by default")
     var disableDefaultScriptingPlugin: Boolean by FreezableVar(false)
 
+    @Argument(
+        value = "-Xapi-mode",
+        valueDescription = "{enable|disable|migration}",
+        description = "Enable api mode, force compiler to report errors an all public API declarations without explicit visibility.\n" +
+                "Use 'migration' level to issue warnings instead of errors."
+    )
+    var apiMode: String by FreezableVar(ApiMode.DISABLED.state)
+
     open fun configureAnalysisFlags(collector: MessageCollector): MutableMap<AnalysisFlag<*>, Any> {
         return HashMap<AnalysisFlag<*>, Any>().apply {
             put(AnalysisFlags.skipMetadataVersionCheck, skipMetadataVersionCheck)
@@ -324,6 +332,10 @@ abstract class CommonCompilerArguments : CommonToolArguments() {
             put(AnalysisFlags.useExperimental, useExperimental?.toList().orEmpty())
             put(AnalysisFlags.explicitApiVersion, apiVersion != null)
             put(AnalysisFlags.allowResultReturnType, allowResultReturnType)
+            ApiMode.fromString(apiMode)?.also { put(AnalysisFlags.apiMode, it) } ?: collector.report(
+                CompilerMessageSeverity.ERROR,
+                "Unknown value for parameter -Xapi-mode: '$apiMode'. Value should be one of ${ApiMode.availableValues()}"
+            )
         }
     }