Simplify bookmark impl by exposing internal values

[zhenlineo]

This makes serialization of the bookmark easier to end users.
End users could serialize and deserialize bookmark in whatever way they like using Set<String> values

Bookmark is defined as follows:

Bookmark {
Set<String> values(); // can be used to serialize bookmark
static Bookmark parse(Set<String> values); // can be used to deserialize bookmark
boolean isEmpty();
}

[michael-simons]

I'd remove static Bookmark merge(Iterable<String> bookmarks); to avoid confusion. It's not needed with .parse and .merge in combination and clutters API (at least to me, maybe that's personal taste).

I'm also a bit confused as I thought we spoke about dumping the bookmarks as byte[] from the driver.

[zhenlineo]

@michael-simons Very good input on the merge methods. Would you think this API will be good enough for your use case if we have merge methods removed?

We talked about toBytes, but it is not very idiomatic to Javascript, where most of objects are directly visible to users. .Net driver gives this solution which gives me some new thoughts. The original purpose to hide Bookmark implementation was to prevent users from using the bookmark content, however if users (OGM and/or Fabric) need to use the content anyway, I see fewer points to hide it.

[michael-simons]

Thanks, Zhen. I'd only remove the static Bookmark merge(Iterable<String> bookmarks);

With the Strings is totally fine with me this way.

[michael-simons]

LGTM! Thanks for your work on that.