feat: add Xcode 15 and visionOS support

[okwasniewski]

Hello,

This PR adds support for Xcode 15 action together with visionOS support.

Apple Vision has an internal Apple codename xros, but the user facing stuff is named visionOS. I've kept user facing stuff with visionOS naming.

I've tested out the code building bgfx examples for visionOS (they obviously didn't compile but the project was generated correctly)

elseif "xros" == _OPTIONS["xcode"] then
	action.xcode.visionOSTargetPlatformVersion = str_or(xrosPlatform, "1.0")
	premake.xcode.toolset = "xros"
	location (path.join(_buildDir, "projects", _ACTION .. "-xros"))
end

[okwasniewski]

Hey, the PR is ready for review