add icons to emphasis button snippets

To demonstrate what's happening with icon colours.

Particularly useful for Hackney Brook :)

mentioned in issue dev/core#5798

Thanks - looks good.

I probably need to add some of the specific cases for each as it's not always inside buttons.. e.g.

.crm-container .crm-i.fa-times,
.crm-container .btn-danger .crm-i,
.crm-container button .fa-times {
  color: var(--crm-icon-alert-color);
}
.crm-container .delete-icon::before,
.crm-container .crm-i.fa-trash::before {
  content: "\f1f8";
  color: var(--crm-icon-alert-color);
}
.crm-container .crm-i.fa-check,
.crm-container .crm-i.fa-check-circle,
.crm-container .btn-success .crm-i,
.crm-container .crm-i.fa-plus-circle {
  color: var(--crm-icon-success-color);
}

mentioned in commit c7c65035

merged

Maybe depends how the other discussion goes, but it would make sense for those declarations to use whatever colour is used for text-success / text-danger

exactly - so in this way we're not really adding new variables, we're renaming the icon variables and applying them to text-*. I like it in a way because it's a bit confusing that some button icons use these colours and some don't.

Needless to say this will all need some thorough testing - preferably with all of the colour / name changes at once.