Do not disable 'redundant visibility modifier' inspection completely in Explicit API mode.

Instead, disable it only for effectively public declarations.

Add tests for this IDE inspection.

compiler/testData/diagnostics/testsWithExplicitApi/mustBeEffectivelyPublic.kt

@@ -1,3 +1,20 @@
 private class Foo {
     fun method() {}
+}
+
+public interface I {
+    public fun bar()
+}
+
+public fun f() {
+    val i = object : I {
+        internal var foo = 0
+        override fun bar() {}
+    }
+    i.foo = 1
+
+    class LocalClass {
+        internal var foo = 0
+    }
+    LocalClass().foo = 1
 }