[3.5] Add platform-switch submodule

[halotroop2288]

Supersedes #9, as that approach did not work correctly.

Modifies commits from #3 to reduce the amount of changes outside the platforms directory.

[hokaze]

Briefly looked at this but am not confident I can review it right now, partly because I'm very tired and partly because the diff github is showing me from this commit is giving me a headache, it understandably has a whole bunch of additions that were already added to the repo ages ago, but I just want to see what's actually been changed here since the original commits from PR #3.

Here's where only using git casually and svn in my day job has left me baffled - I have no idea how I'm supposed to check what has actually been changed in this PR, or if that's even possible, as there's no way the diff I'm being shown is accurate.

Ideally I'd just want a diff of what's actually changed, and while I could probably stitch something together by grabbing diffs from older PRs, that sounds like a huge headache - hoping you know of a better way?

(Either way, looks like I'll be giving myself through a quick refresher on some git functionality I've never had a reason to use and not touched since university)

[halotroop2288]

there's no way the diff I'm being shown is accurate.

That's because you're expecting it to be the difference between Homebrodot/main/3.5 and halotroop2288/pr/3.5 but this PR is targeting the new branch Homebrodot/3.5 which does not have any of the Homebrodot changes.
It would be impossible to merge this into the main/3.5 branch because it rewrites the history.

[hokaze]

Far as I can tell the submodule to https://github.com/Homebrodot/platform-switch all looks good, and the new 3.5 branch has the main/3.5 switch-specific core/non-platform changes it needs.

[hokaze]

Per discussion on the main/3.5 branch...
f950ebd#r138181091
...can potentially avoid having any modifications to this file at all to add in Switch in support if we override OS::get_resource_path for the switch

That'll be a change that'll need doing on the platform-switch submodule repo rather than here, but wanted a note to remain on this branch as reminder that we should be able to remove it in a future update.