jsxref: derive namespace-strip aliases from page types instead of a hard-coded list

[caugner]

Summary

jsxref lets authors address class-style namespace members without the namespace prefix (e.g. {{jsxref("Collator")}} → Intl/Collator). Today the eligible namespaces are a hard-coded list:

const NAMESPACE_PREFIXES: &[&str] = &["Global_Objects/Intl/", "Global_Objects/Temporal/"];

This is pragmatic — only Intl and Temporal have class-style children today — but it has to be updated by hand whenever a new such namespace appears.

Proposal

Derive the aliases from page types instead. When building the index, strip the namespace prefix for a page only when:

• the parent page is a JavascriptNamespace, and
• the child page is a JavascriptClass.

This naturally includes Intl/Temporal (class children) and excludes Math/JSON/Reflect (whose children are JavascriptStaticMethod/JavascriptStaticDataProperty/etc.), which is exactly the distinction the hard-coded list draws by hand. It also future-proofs against new namespaces without a code change.

The PageType variants already exist (JavascriptNamespace, JavascriptClass, …), and the index is built from en-US only, where page types are reliably set. The main work is threading the parent and child page types into index_one.

Notes

• Low priority / future-proofing: only two namespaces qualify today.
• The hard-coded list has a self-explanatory doc comment, so behavior is unchanged until this lands.

Follow-up from the review of #715.