Remove unnecessary std usage from bindgen in writer.rs

[ajw221]

Recently ran into some issues while attempting to use windows-bindgen in a no_std crate. The generated code contains almost all ::core usage except for a few areas where ::std is used instead.

[ajw221]

@microsoft-github-policy-service agree

@microsoft-github-policy-service agree

[kennykerr]

Maybe we need a dedicated test crate that "proves" this works for no_std to avoid future regressions, unless all of test_standalone can be marked no_std.

[kennykerr]

This would also depend on the windows-core being no_std. While I think this is a good idea in general, this will require a bit more of a systematic approach. Why don't you start by creating an issue and we can discuss.