Add Data.Artifacts to css.Build and js.Build

[bep]

Artifacts are the additional output files published as part of the build:
source maps and files emitted by ESBuild's file loader (e.g. fonts). Each
artifact provides Permalink, RelPermalink and MediaType, so e.g. font
preload links can be constructed in templates.

Also add media type definitions for source maps (application/source-map),
font/woff and font/woff2.

Fixes #15173

Co-Authored-By: Claude Fable 5 noreply@anthropic.com

[Copilot]

Pull request overview

This PR exposes additional output files produced during css.Build/js.Build (e.g. source maps and ESBuild file-loader outputs like fonts) to templates via Resource.Data.Artifacts, and adds default media types needed to label these artifacts correctly.

Changes:

• Add resources.Artifact and populate ResourceTransformationCtx.Data["Artifacts"] during ESBuild processing.
• Add integration tests validating artifact presence/links for both css.Build and js.Build.
• Extend builtin media types to include source maps and WOFF/WOFF2.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tpl/css/build_integration_test.go	Adds coverage for .Data.Artifacts in css.Build, including fonts and external sourcemap.
resources/transform.go	Clarifies Data serialization expectations and fixes related documentation wording (plus a comment typo).
resources/resource_transformers/js/js_integration_test.go	Adds coverage for .Data.Artifacts in js.Build with external sourcemap.
resources/resource_transformers/js/build.go	Collects/publishes artifacts from ESBuild output and exposes them via .Data.Artifacts.
resources/artifact.go	Introduces the resources.Artifact interface and implementation returned to templates.
media/config_test.go	Updates default media type tests for new builtin types.
media/builtin.go	Adds builtin media types and suffix mappings for source maps and WOFF/WOFF2.

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