Add more explicit types for the default theme

[thecrypticace]

Fixes #8728

[RobinMalfait]

I wonder if we could generate types on the fly when we are in watch mode so that we also catch types from the user config (and deeply nested resolved configs) that would be kind of cool.

I got worried for a second that the types weren't using all the shapes they could use (e.g. fontSize allows multiple forms) and we only used a single record. But then I realized that this is "just" for the tailwindcss/defaultTheme import itself which I think is good right now.

For the functions we could try to resolve the default config first so that the functions are gone, but then the issue is that it can look like you can just do defaultTheme.backdropBlur.lg but that's not the case because of that function so right now I think this makes sense.

[RobinMalfait]

Looks good to me.