Expose Font Awesome icons to core icon API

[laryn]

This PR does the same for the Bootstrap Icons module and should be pretty straightforward to adapt for Font Awesome:

• Issue #3: Expose Bootstrap icons to core icon API. bootstrap_icons#4

[yorkshire-pudding]

Thanks @laryn - happy to accept a PR or I will try and get to this sometime soon.

[laryn]

@yorkshire-pudding Sure, I'll try to prepare a PR for your review.

[laryn]

@yorkshire-pudding Ready for review. This is locally with Icon Browser:

font-awesome-in-icon-browser.mp4

[yorkshire-pudding]

Thanks @laryn

I've tested this and it looks great.

I don't think it is related to this PR, but I'm getting warnings on the icon browser page when I click an icon:

Warning: Undefined global variable $theme_key in _icon_from_theme() (line 137 of /app/docroot/core/includes/icon.inc).
Warning: Undefined array key "" in _icon_from_theme() (line 158 of /app/docroot/core/includes/icon.inc).

Seems to also happen for clicking on core icons so I've opened a ticket in the icon browser repo - backdrop-contrib/icon_browser#12

I'll probably wait until the 1.28.0 release to merge and release this

Many thanks