Add Mark inline formatting

[geriux]

This PR is a follow-up of #939 to wrap up adding Mark formatting support.

To test this feature, use the iOS build from this PR that uses this feature.

Fix

Adds Mark formatting capabilities.

Test

For test cases, you can check the description of this PR.

Review

@antonis

Make sure strings will be translated:

• If there are new strings that have to be translated, I have added them to the client's strings.xml as a part of the integration PR.

[geriux]

Hey there @hypest@mchowning 👋

I'm having an issue with this feature and I saw you have worked on this project before, I was wondering if any of you might have some insight 😄

Currently, if you have a word typed in, and an empty <mark> tag at the end, if you focus at the end to write something within the tag, it will let you add content but while you do so, the first word is wrapped by another <mark> tag with the CSS attributes of the original mark tag. The desired result would be to leave the first word as it was and be able to type content within the mark tag that's at the end.

Screenrecorder-2021-11-17-10-47-01-827.mp4

Have you seen this before? I updated the demo app content to show the current issue. Any guidance would be appreciated. Thanks!

[hypest]

👋 @geriux , thanks for the ping!

Haven't really dug deeply into this yet, but thought of sharing this in case it helps in the meantime: I wonder if there's some mixup with inline and block level elements handling here that leads to that separate to appear. For example, I see that it's the blockFormatter used here instead of the inlineFormatter. I understand that the mark tag is an inline-level HTML tag, right? So, I'd expect to only see it being handled by the inline elements related classes. Again, I haven't tried to really debug this so, take the above with a grain of salt :)

[antonis]

Great work @geriux 👍
I tested with the Gutenberg PR and everything works as expected. The code also LGTM 🎉

I added a couple of comments that do not affect the code functionally :)