Set appropriate visiblity for methods/fields in NativeConverter

NativeConverter and Charset*ICU classes were in the different java
package. Now they are in the same package, and the visiblity
of methods/fields could be more restrictive.

Bug: 138994281
Test: m droid
Change-Id: Ic8d7c25b55b74130167fa1bdadd7cc5260941ead
1 file changed