refactor: drop the remaining docusaurus names from identifiers and comments (#589)

Follow-up to #588.

- rename `DocusaurusSidebarItem` -> `SidebarSourceItem`, `fromDocusaurus` -> `fromSidebarSource`, `docusaurusSidebars` -> `sidebarSources`
- reword comments and READMEs that described behaviour by comparison with docusaurus; fix the stale note in `sites/docs/src/config/api.ts`
- drop `.docusaurus/` from `.gitignore`

No functional change. `pnpm check` has 0 errors and `pnpm build` still builds 6690 pages.

<!-- cloudflare-preview --> Preview: https://pr-589.docs-gitea-com.pages.dev

Reviewed-on: https://gitea.com/gitea/docs/pulls/589
Reviewed-by: silverwind <[email protected]>

packages/content-loader/src/sidebar.ts

@@ -1,6 +1,6 @@
 /**
  * Builds one sidebar per (product, version, language) out of the loaded pages,
- * reproducing what docusaurus derived from `_category_.json` and from the
+ * deriving it from `_category_.json` and from the
  * handwritten sidebar files of the runner docs.
  */
 
@@ -44,12 +44,12 @@ export interface SidebarGroup {
 
 export type SidebarEntry = SidebarLink | SidebarGroup;
 
-/** A docusaurus sidebar file, as used by the runner docs. */
-export type DocusaurusSidebarItem =
+/** A hand written sidebar file, as used by the runner docs. */
+export type SidebarSourceItem =
   | string
   | { type: 'doc'; id: string; label?: string }
   | { type: 'autogenerated'; dirName: string }
-  | { type: 'category'; label: string; collapsed?: boolean; items: DocusaurusSidebarItem[] };
+  | { type: 'category'; label: string; collapsed?: boolean; items: SidebarSourceItem[] };
 
 const last = Number.MAX_SAFE_INTEGER;
 
@@ -66,11 +66,11 @@ function labelFromDirname(name: string): string {
 
 /**
  * Builds the sidebars of every group of pages, keyed by the route prefix of the
- * group. `manual` provides the docusaurus sidebar of the groups that ship one.
+ * group. `manual` provides the hand written sidebar of the groups that ship one.
  */
 export function buildSidebars(
   pages: SidebarPage[],
-  manual: Map<string, DocusaurusSidebarItem[]> = new Map(),
+  manual: Map<string, SidebarSourceItem[]> = new Map(),
 ): Map<string, SidebarEntry[]> {
   const groups = new Map<string, SidebarPage[]>();
   for (const page of pages) {
@@ -84,19 +84,19 @@ export function buildSidebars(
     const key = `${groupPages[0]!.meta.product}@${groupPages[0]!.meta.version}`;
     const items = manual.get(key);
     const tree = treeOf(groupPages);
-    sidebars.set(prefix, items ? fromDocusaurus(items, groupPages, tree) : tree.build(''));
+    sidebars.set(prefix, items ? fromSidebarSource(items, groupPages, tree) : tree.build(''));
   }
   return sidebars;
 }
 
 interface Tree {
-  /** Entries of a directory, ordered as docusaurus ordered them. */
+  /** Entries of a directory, ordered by their position. */
   build(dir: string): SidebarEntry[];
   /** Localized label of a directory, from its `_category_.json`. */
   label(dir: string): string;
 }
 
-/** Sidebar of a directory tree, ordered by `sidebar_position` as docusaurus did. */
+/** Sidebar of a directory tree, ordered by `sidebar_position`. */
 function treeOf(pages: SidebarPage[]): Tree {
   const categories = new Map<string, SidebarPage>();
   for (const page of pages) {
@@ -148,9 +148,9 @@ function treeOf(pages: SidebarPage[]): Tree {
   return { build, label };
 }
 
-/** Sidebar described by a docusaurus sidebar file, used by the runner docs. */
-function fromDocusaurus(
-  items: DocusaurusSidebarItem[],
+/** Sidebar described by a hand written sidebar file, used by the runner docs. */
+function fromSidebarSource(
+  items: SidebarSourceItem[],
   pages: SidebarPage[],
   tree: Tree,
 ): SidebarEntry[] {
@@ -159,7 +159,7 @@ function fromDocusaurus(
     byDocId.set([page.meta.dir, page.meta.name].filter(Boolean).join('/'), page);
   }
 
-  const convert = (item: DocusaurusSidebarItem): SidebarEntry | undefined => {
+  const convert = (item: SidebarSourceItem): SidebarEntry | undefined => {
     if (typeof item === 'string') {
       const page = byDocId.get(item);
       return page && link(page);
@@ -167,7 +167,7 @@ function fromDocusaurus(
     if (item.type === 'doc') {
       const page = byDocId.get(item.id);
       // the label of the sidebar file is english, the title of a translated
-      // page is already localized (docusaurus translated it from the json)
+      // page is already localized (translated from the json)
       return page && link(page, page.meta.locale === defaultLocale ? (item.label ?? page.title) : page.title);
     }
     if (item.type === 'autogenerated') {
@@ -182,7 +182,7 @@ function fromDocusaurus(
     }
 
     // a category whose only child is an autogenerated directory keeps the
-    // translated label of the directory, like the docusaurus sidebars did
+    // translated label of the directory, like the sidebar files do
     const single =
       item.items.length === 1 && typeof item.items[0] === 'object' && 'dirName' in item.items[0]
         ? item.items[0]