The PR introduces a few doc content rendering fixes:
- Fix highlighted section heading styles (regression from #59965).
- Convert JSDoc links within 'Usage Notes' sections to HTML and render them.
- Add IDs to doc content headings. This, by itself, makes these headings available in the page ToC.
PR Close#60116
To increase the ease of development we are moving @angular/docs into the adev directory within this repo. While
we are doing this to improve our development experience in the short term, efforts are also in place
to maintain a division between this @angular/docs (shared) code and adev itself, so that it can be extracted
back out in the future when components is ready to leverage it as well.
PR Close#57132
