[clang-tools-extra][docs] Add previous versions of `clang-tools-extra` site in index.html.

[vbvictor]

For now, when user visit clang-tools-extra main page https://clang.llvm.org/extra/index.html, he can only see WIP version of current developing LLVM branch. There is no good way to find release notes from previous releases, e.g. 19th, 20th, 21st.

By googling, I could find snapshot of 16th release of clang-tools-extra - https://releases.llvm.org/16.0.0/tools/clang/tools/extra/docs/index.html.
But if I change 16 to any other number - there is no page.

I propose making a list in index.html or a dedicated page that would have working links to previous versions of clang-tools-extra so that a user could read release-notes and documentation of clang-tool that they currently use.

[weirdsmiley]

@vbvictor can I take this up? It looks like there hasn't been any published released notes since 16.0.0 (for N.0.0 minor versions). There are some other releases at 19.1.0 and 20.1.0. Is there a policy for which version a release note is added?

[vbvictor]

Hi, thank you for volunteering, appreciate it.
One problem is that I don't have a vision right now of how the site should look like (maybe even an RFC needed).

These are problems I'd like to solve in general:

1. Easy access to older ReleaseNotes (probably to 2-3 releases back). I think they could go right after "(In Progress) Release Notes". We need to think of a way to update those links automatically after a new release.
2. Easy access to older versions of clang-tools-extra site. One way to solve this is to navigate through older ReleaseNotes added in #1. Another solution is to keep somewhere a list of older-version of the clang-tools-extra site.

You can work on them, but it may take some time in the PR to form a consensus.

Is there a policy for which version a release note is added?

I found that other ReleaseNotes are located here https://releases.llvm.org/ (under Documentation).