Fix resolution of imported CSS files in Vite SSR builds

[AlemTuzlak]

It seems this change makes the below mentioned issue go away and seems to generate the correct tailwindcss output file durring the ssr build. Big shoutout to @rossipedia for figuring this out.

I think you guys might want to take this over and own it as I'm not sure about other implications and if it breaks any other framework.

Fixes #15237

[thecrypticace]

Ah this is interesting. I was just heads down looking into this and found it was related to SSR when the user config explicitly overrides ssr.resolve.conditions but came up with a different fix:

ssrConfig: {
  resolve: {
    conditions: ['style', 'development|production'],
  },
},

This fixes it in Vite 5 but isn't needed at all Vite 6 because it just works as expected. Gonna look into the aliasOnly thing a bit because that would be a cleaner fix assuming it's the right one.

[thecrypticace]

I think this fix is the correct one. Looking into it (and the original problem) the aliasOnly flag causes Vite to consider aliases but not SSR stuff, externals, fs paths, etc… which shouldn't be a problem here.

Just needs tests (don't worry I'm gonna add these)!