Two adjacent links with the same URL should be merged

[zoltanhosszu]

This should not be possible:

I typed the text, pasted the link to link1, and then selected both words and pasted again. We should merge these two links nodes on paste.

[yanfroes]

Hi @zoltanhosszu , I created a PR #719 to fix this, but I wasn't 100% sure what is the expected behavior in the scenario below:
For example, I already have a link in one of the selections:
Testing <a href="https://link1.com">multiple</a> links
If I select "multiple links" and paste a different link (https://link2.com), what should be the behavior?
A: Testing <a href="https://link2.com">multiple links</a>
B: Testing <a href="https://link1.com">multiple</a><a href="https://link2.com"> links</a>

In #719 I implemented the A behavior.

FYI: this would be the result today:
Testing <a href="https://link2.com">multiple</a><a href="https://link2.com"> links</a>