Add the react-native-hr library to GB mobile

[pinarol]

This is a simple PR that adds the react-native-hr library to GB mobile. It will be used by the nextpage block. Usage can be found in this PR.

I've updated the submodule ref to point to the gutenberg branch that uses the new Hr element. So you can open the demo app and verify that there is a text-surrounding line in the Page break element which is brought us by this new Hr element:

[hypest]

👋 @pinarol , is there perhaps a GB-web side branch or PR to link with in this PR? I don't see GB-web ref being updated or a PR referenced so, not sure how to test this one? Thanks!

[hypest]

This PR is a followup from #209 so, let's wait for #209 before moving on with this one. Is that OK @pinarol ? Thanks!

[pinarol]

right let's wait for #209 firstly

[pinarol]

this is ready to review @hypest I updated the GB-web ref to include the example usage

[etoledom]

Hey @pinarol - This is looking great! 🎉

I couldn't find the Gutenberg side PR, though.
Can we have a review on that side before merging this one?

Thank you!

[pinarol]

Hi @etoledom here I opened it, I didn't open it before because it won't compile without this change so this PR needs to be merged first, but yes it'd be better if reviewers at least see the related change. 👍

[pinarol]

@hypest I thought the gutenberg PR will not compile without the new lib introduced with this PR but it looks like tests have passed. So should I merge this one first?

[hypest]

I notice that the Gutenberg side PR only touches .native files and as of WordPress/gutenberg#11318 Travis will happily say everything's fine. So, the only way to test if the GB side PR will break the mobile tests is to try it manually (try using that GB branch against mobile master that is).

Now, we do actually know that the import on the GB side will break against current mobile master in some way so, let's review and give the green light here and then quickly merge the GB side, update this PR's ref and merge it too. The total disruption to mobile master will be small. WDYT?

[pinarol]

@hypest I agree, it looks like it won't be a problem as soon as I'm quick between PR merges. So once PR reviews are done I can just merge GB PR and then update this PR's ref and merge it too 👍

[etoledom]

It looks great and all tests are passing (so far 😅)
@pinarol - All yours to do the merge magic!

[pinarol]

We know that there's a known issue with travis checks currently and we are working on it, but we decided to merge this immediately in order not to cause compile errors on local working environments since a new library is introduced with this PR and it is already imported from the gutenberg submodule.