Global Styles: Duplicate slugs aren't handled correctly

[ajlende]

Taken from #56661 (comment).

#53558 may be related; however, that issue is dealing with duplicate "size" properties instead of duplicate "slug" properties that are being described here.

Description

Generating the global stylesheet doesn't filter out duplicates, so the later CSS overrides the earlier. This example shows the issue within a single theme.json settings.typography.fontSizes.

{
	"name": "Display xl2",
	"slug": "Display-xl",
	"size": "296px"
},
{
	"name": "Display xl",
	"slug": "Display-xl",
	"size": "96px"
},

The issue also extends to overriding defaults as well. You should be able to override default values because prevent_override is false in PRESETS_METADATA, but for some reason that doesn't work. The core defaults are shown and used instead when including these in the theme.json settings.typography.fontSizes presets.

{
	"name": "Override Small",
	"slug": "small",
	"size": "26px"
},
{
	"name": "Override Medium",
	"slug": "medium",
	"size": "40px"
},
{
	"name": "Override Large",
	"slug": "large",
	"size": "72px"
},

[github-actions]

Hi,
This issue has gone 30 days without any activity. This means it is time for a check-in to make sure it is still relevant. If you are still experiencing this issue with the latest versions, you can help the project by responding to confirm the problem and by providing any updated reproduction steps.
Thanks for helping out.