[ObjC] Use more complete imports

Import both the public and private header into impls when the
private is needed.

Also update the tests to use more complete imports.

PiperOrigin-RevId: 671388271
diff --git a/objectivec/GPBUnknownFields.m b/objectivec/GPBUnknownFields.m
index dc004b3..0c53a72 100644
--- a/objectivec/GPBUnknownFields.m
+++ b/objectivec/GPBUnknownFields.m
@@ -6,9 +6,11 @@
 // https://developers.google.com/open-source/licenses/bsd
 
 #import "GPBUnknownFields.h"
+#import "GPBUnknownFields_PackagePrivate.h"
 
 #import <Foundation/Foundation.h>
 
+#import "GPBCodedInputStream.h"
 #import "GPBCodedInputStream_PackagePrivate.h"
 #import "GPBCodedOutputStream.h"
 #import "GPBCodedOutputStream_PackagePrivate.h"
@@ -16,9 +18,9 @@
 #import "GPBMessage.h"
 #import "GPBMessage_PackagePrivate.h"
 #import "GPBUnknownField.h"
+#import "GPBUnknownFieldSet.h"
 #import "GPBUnknownFieldSet_PackagePrivate.h"
 #import "GPBUnknownField_PackagePrivate.h"
-#import "GPBUnknownFields_PackagePrivate.h"
 #import "GPBWireFormat.h"
 
 #define CHECK_FIELD_NUMBER(number)                                                      \