[FIX] web_editor: link don't duplicate child text

If we applied a link eg. on:

```
<span>hello <b>world</b></span>
```

The system actually gets the "label": hello worldworld because there is
3 nodes:

 text node: hello
 element node: `<b>world</b>`
 text node: world

Also since "hello worldworld" is different than "hello world",
instead of just keeping existing nodes and adding the link, the system
would replace the selected range by:

 `<span><a>hello worldworld</a></span>'

instead of:

 `<span><a>hello </a><b><a>world</a></b></span>`

This commit ignores element nodes when creating a new link, since when
getting the label of the link from the selection, only the text nodes
insides the element nodes have any interest.

There was a second issue because if we had:

```
<i><a href="hello">world</a></i>!
```

and tried to put a link over "world!", the code would decide: "world" is
inside a link so we will just update that link.

Thus we would get:

```
<i><a href="hello">world!</a></i>!
```

instead of:

```
<i><a href="hello">world</a></i><a href="hello">!</a>
```

opw-1848351
closes #25187