Theme JSON: cached resolved URIs

[ramonjd]

Syncing WordPress/gutenberg#66155

Trac ticket: https://core.trac.wordpress.org/ticket/62261

What?

Implement "pretty basic caching" for resolved theme URIs in WP_Theme_JSON_Resolver::get_resolved_theme_uris.

Why?

The intention to improve performance, even if slightly.

WP_Theme_JSON_Resolver::get_resolved_theme_uris, and WP_Theme_JSON_Resolver::resolve_theme_file_uris which calls it, is fired multiple times in a single session to:

1. Generate styles
2. Deliver resolved URIs in a global styles controller response.

Here are some preliminary, but pretty inconclusive performance results (higher response time is worse):

Uncached	This PR (cached)

I'd expect results will become more pronounced as other relative paths are introduced, e.g., fonts, and more blocks support background images.

Cached data is not be stored persistently across page loads.

How?

Simple object caching.

Testing Instructions

PHP CI tests should pass.

Create a theme.json with background image paths defined for several blocks.

Ensure these appear as expected in the editor and frontend.

In the theme.json file, replace one or several paths with new asset paths. Check that the styles have been updated and the editor/frontend looks good.

Here is some test JSON based on current assets in TT5:

{
	"$schema": "../../schemas/json/theme.json",
	"version": 3,
	"settings": {
		"appearanceTools": true
	},
	"styles": {
		"background": {
			"backgroundImage": {
				"url": "file:./assets/images/category-anthuriums.webp"
			}
		},
		"blocks": {
			"core/group": {
				"background": {
					"backgroundImage": {
						"url": "file:./assets/images/category-cactus.webp"
					}
				}
			},
			"core/post-content": {
				"background": {
					"backgroundImage": {
						"url": "file:./assets/images/hero-podcast.webp"
					}
				}
			},
			"core/quote": {
				"background": {
					"backgroundImage": {
						"url": "file:./assets/images/category-sunflowers.webp"
					}
				}
			},
			"core/pullquote": {
				"background": {
					"backgroundImage": {
						"url": "file:./assets/images/dallas-creek-square.webp"
					}
				}
			}
		}
	}
}

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[ramonjd]

Might be premature.

Looks like there's a small impact on performance on TT4

https://github.com/WordPress/wordpress-develop/actions/runs/11432958553?pr=7596

I'll run again as the tests vary between commits, e.g., https://github.com/WordPress/wordpress-develop/actions/runs/11432437736?pr=7596