[cross_file] Document mime type is not made for io implementations

[ValentinVignal]

Fixesflutter/flutter#93379

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[ValentinVignal]

That "fix" seems a bit "small" / "light" to me.

Can you help me figure out what else should be good to be done about that?

[ditman]

@ValentinVignal this is very similar to #4416, any chance of collaborating with @andreacioni to render all doc improvements to cross_file in a single, coordinated push? Thanks!

[andreacioni]

Hello, no problem for me. I can integrate your changes in my PR @ValentinVignal .

Let me know if this solution works for you 😊

[ValentinVignal]

Should I create the PR on your branch then @andreacioni ?

[andreacioni]

Yeah, I think it would work. Feel free to open it.

[ValentinVignal]

Closing in favor of andreacioni#1