[FIX] web_editor: prevent having wrong connectors when an icon change

Steps to reproduce the bug:
- Drop a block steps on a page
- Change one of the icons
- Change the color of the icon

=> The connectors are not correct anymore.

This is due to [this commit] changing the tag `<i class="fa...` to a
`<span class="fa...` when the user replaces an icon. The steps options
assume that `<i/>` tags will remain `<i/>` tags (as it was before
[this commit]). We should not change the tagName when changing the icon
of an `<i/>` tag. This is likely to break (s)css, options, public
widgets, ... This commit fixes this bug by ensuring that `<i/>` tags do
not become `<span>` tags when replacing the icon. Moreover it allows not
to recreate an editor when you change the icon.

[this commit]: https://github.com/odoo/odoo/commit/7fd0698cf765a79959566b51e33cb76bff83d344



task-3068834
opw-3123850

closes odoo/odoo#106316

Signed-off-by: Outagant Mehdi (mou) <mou@odoo.com>