[docs] Update supported platforms documentation

[uilianries]

Summary

Updated the documentation page with the current supported platforms and their information.

Motivation

closes #29018

/cc @Andrej730

Details

---

• Read the contributing guidelines
• Checked that this PR is not a duplicate: list of PRs by recipe
• If this is a bug fix, please link related issue or provide bug details
• Tested locally with at least one configuration using a recent version of Conan

---

Add a 👍 reaction to pull requests you find important to help the team prioritize, thanks!

[jcar87]

arm64 Windows CI only runs on a subset of ~400 recipes so far.

[uilianries]

Added a note about that restriction on the commit 3a5f2ce

[Andrej730]

Hi! Thank you for updating this. Could docs also include a general workflow on deciding what platforms will be used for a recipe? Is there some place where currently used platforms are declared for each recipe (I've searched recipes folders but there doesn't seem to be anything related)?

See the comment below - it seems in some cases there are multiple builds for different compiler versions, different cppstd and sometimes some builds are just missing. And I was trying to understand the guidelines when there are more or less builds will be available.

Also for Windows it seems there is a practice to build for multiple compiler version (e.g. 192, 193, 194 builds in conan.io/center/recipes/gmp). Or separate cppstd=17 and cppstd=gnu17 builds on Mac also for gmp.
And for some recipes some builds are missing - e.g. conan.io/center/recipes/opencascade missing mac/windows arm64.