Adding set/remove link methods.

[etoledom]

This PR is one step to implement Links managing in Gutenberg mobile.

The current implementation on RCTAztecView is:

//To set a link for the selected text:
setLink("link-to-add.com")

//To set a link without selecting text, with the given title (or text):
setLink("link-to-add.com", "title")

//To remove a link currently under the cursor (selected or not selected):
removeLink()

To give back the information of the current url for the link was quite challenging. My initial intention was to implement a function like getLinkAttributes(callback) that we could call when the information is needed. But I didn't find a way to make it work (Native UI Components seems to be quite different to plane Native Module Components).

To solve this problem and to be able to give back that information to the JS side, I decided to use the same strategy used on onActiveFormatsChange, but giving more information.

I added a onActiveFormatAttributesChange, with a current implementation with just links.
If you select or navigate the cursor to anywhere with a link format, onActiveFormatAttributesChange will be called with this info:

link: {
    isActive: true
    url: "wp.com", 
}

For any other time, it will be called with:

link: {
    isActive: false 
}

This could be used for formats too and potentially replace onActiveFormatsChange.

@Tug let me know what do you think about it. We can still try to find another way, but I didn't find anyway to use callbacks (or promises) to ask and get info back from native code.

In the branch gutenberg/rnmobile/test-links you can find a testing code, and see how it looks:
WordPress/gutenberg@mobile...rnmobile/test-links

[etoledom]

cc @daniloercoli since the Android side is also related.

[Tug]

Do you think we could use applyFormat instead of setLink and removeLink to set and remove a link?

[Tug]

oh right, applyFormat only accepts a string (the format) as parameter, I guess we need something else for the url 👍

[Tug]

Code and logic looks good to me 👍
However I'm no expert in swift so I think someone else should double check

[etoledom]

Thank you @Tug !

@diegoreymendez could you take a look to the native side please?
Thank you :)

[diegoreymendez]

Just two comments for your consideration.

[diegoreymendez]

The initial character in the string here is capitalized, but not for the others. I'd suggest to standardize for clarity.

[diegoreymendez]

Considering that:

1. This method is only being used in the compactMap() call above as far as I can tell.
2. This method is effectively equivalent to formatStringMap[identifier] if we need the format string from any other place in our code.

I'm wondering if we really need this to be a method and not just a closure, such as { formatStringMap[$0] } above (untested but you get the idea).

[diegoreymendez]

By the way, code-wise the native end of it looks clean to me. I don't see anything off about it.