feat(v2): allow specifying TOC max depth (themeConfig + frontMatter) (#5578)

* feat: add all TOC levels to MDX loader

* feat: add theme-level config for heading depth

* test: add remark MDX loader test

* fix: limit maxDepth validation to H2 - H6

* refactor: set default `maxDepth` using `joi`

* refactor: `maxDepth` -> `maxHeadingLevel

* refactor: invert underlying TOC depth API

* refactor: make TOC algorithm level-aware

* feat: add support for per-doc TOC heading levels

* feat: support document-level heading levels for blog

* fix: correct validation for toc level frontmatter

* fix: ensure TOC doesn't generate redundant DOM

* perf: simpler TOC heading search alg

* docs: document heading level props for `TOCInline`

* Update website/docs/guides/markdown-features/markdown-features-inline-toc.mdx

Co-authored-by: HonkingGoose <34918129+HonkingGoose@users.noreply.github.com>

* docs: fix docs (again)

* create dedicated  test file for heading searching logic: exhaustive tests will be simpler to write

* toc search: add real-world test

* fix test

* add dogfooding tests for toc min/max

* add test for min/max toc frontmatter

* reverse min/max order

* add theme minHeadingLevel + tests

* simpler TOC rendering logic

* simplify TOC implementation (temp, WIP)

* reverse unnatural order for minHeadingLevel/maxHeadingLevel

* add TOC dogfooding tests to all content plugins

* expose toc min/max heading level frontmatter to all 3 content plugins

* refactor blogLayout: accept toc ReactElement directly

* move toc utils to theme-common

* add tests for filterTOC

* create new generic TOCItems component

* useless css file copied

* fix toc highlighting className conflicts

* update doc

* fix types

Co-authored-by: HonkingGoose <34918129+HonkingGoose@users.noreply.github.com>
Co-authored-by: slorber <lorber.sebastien@gmail.com>

packages/docusaurus-types/src/index.d.ts

@@ -421,4 +421,5 @@ export interface TOCItem {
   readonly value: string;
   readonly id: string;
   readonly children: TOCItem[];
+  readonly level: number;
 }