[FIX] extensions: icon_role fa icons

[samueljlieber]

Task: #3912370 [FIX] suggested from https://github.com/odoo/documentation/pull/9065#discussion_r1590702515

This PR fixes the FontAwesome icon_role implementation by automatically including the fa main class in the <i> class attribute when rendered. This was suggested to match the 16.0 Odoo UI oi implementation.

This PR should be merged after #9065.

[robodoo]

Pull request status dashboard.

[samueljlieber]

Hi @odoo/design-doc-review, just checking if you have any comments on this PR before I merge. Thank you!

[AntoineVDV]

Elisabeth is off at the moment and it's a change small enough to just move forward ;)

[samueljlieber]

@robodoo r+