Change NO_EXPLICIT_VISIBILITY_IN_API_MODE diagnostic range to 'declaration modifiers + name'.

Motivation: missing visibility modifier is an error in visibility modifiers list, so we should highlight this list.
Including a name in the range is convenient for using alt+enter (you don't have to move cursor from name to fun/class/val keyword)

 Also change NO_EXPLICIT_RETURN_TYPE_IN_API_MODE diagnostic range to 'declaration name' to match corresponding IDE inspection.

Fix stylistic problems and typos after review

compiler/testData/diagnostics/testsWithExplicitApi/companionObject.kt

@@ -1,3 +1,13 @@
+// SKIP_TXT
+
 public class Bar {
-    companion <!NO_EXPLICIT_VISIBILITY_IN_API_MODE!>object<!> {}
+    <!NO_EXPLICIT_VISIBILITY_IN_API_MODE!>companion object<!> {}
+}
+
+public class Bar2 {
+    <!NO_EXPLICIT_VISIBILITY_IN_API_MODE!>companion object MyCompanion<!> {}
+}
+
+public class Bar3 {
+    <!NO_EXPLICIT_VISIBILITY_IN_API_MODE!>object NestedObject<!> {}
 }