Camera: modify metadata visibility attributes

Camera: modify metadata visibility attributes

So we can better describe whether a key should present in java or
native API.

Here are all possbile visibility values:
public      = visible in both Java/NDK public API
ndk_public  = visible in NDK API, @hide in java API
             (mostly source of synthethic keys)
java_public = visible in public java API, not present in NDK
             (mostly synthetic keys or features not supported
              in NDK)
hidden      = @hide in java API, not visible in NDK
system      = not defined in any API.

Bug: 27102995
Change-Id: Ib5163b0aba62126dfe3d72ec62a24136ce206b17