Fall back when social image Glide fails

[edalzell]

Summary

• When glide:generate can't produce a social image, fall back to the raw asset URL so og:image / twitter:image still render. This covers formats the configured image driver can't manipulate (e.g. SVG on GD) as well as files that fail to decode.
• Adds a regression test covering both fallback reasons across the Antlers, Blade and Blade Components views.

Fixes #659

Test plan

• Meta tags for a normal JPG social image still use Glide presets
• SVG social image outputs og:image and twitter:image pointing at the raw asset (no /img/asset/ Glide URL)
• Corrupt / undecodable raster social image outputs og:image and twitter:image pointing at the raw asset
• vendor/bin/phpunit --filter='social_image'

[duncanmcclean]

Thanks for the PR. I've pushed up a handful of changes:

• Retargeted the PR at 7.x and merged it in.
• Removed the gif/svg allowlist from SeoProTags The glide:generate tag already returns the raw asset URL for formats the configured driver can't manipulate, and drops any item it fails to decode.
• I couldn't replicate the GIF failure. Statamic pins league/glide ^3, which pulls Intervention 3.9, and that decodes and resizes animated gifs fine. The "Failed to decode GIF format" message in Social meta images fail (or disappear) when Glide cannot process the asset #659 doesn't exist in Intervention 3, so I suspect that was from a different setup.
• Combined tests using a data provider covering various failure reasons.
• Removed the site-localized fixture copies. Only MetaTagTest uses them, and it runs against the site fixture.

I'll merge and tag a release shortly.