`cargo fix`: Automatically try applying non-MachineApplicable suggestions

[estebank]

In the same spirit as the following environment variable

cargo/src/cargo/ops/fix.rs

Line 419 in dc83ead

let fix_mode = env::var_os("__CARGO_FIX_YOLO")

cargo fix could try first applying all suggestions and if it fails applying only the MachineApplicable ones. This could be problematic depending on the codebase size due to compilation times, but may be it could be worked around by keeping rustc statistics of prior runs and only do this if compile times are short "enough".

[epage]

Interactive mode (#11125) could at least be a first step towards applying other suggestions.

[briansmith]

cargo fix could try first applying all suggestions and if it fails applying only the MachineApplicable ones.

One reason a lint would be marked as something other than MachineApplicable is that its suggestions are sometimes incorrect, namely MaybeIncorrect.

Sometimes they are dangerously incorrect but where the compiler may accept the code. Issues for such lints are labeled l-suggestion-causes-bug. These suggestions should not be applied automatically unless opted into using a mechanism like the one being discussed in issue #13028.

There is another class of buggy lint where the issues are I-suggestion-causes-error where the compiler doesn't accept the suggested code. I guess this is potentially less dangerous. However, it is likely that a I-suggestion-causes-error bug is actually a I-suggestion-causes-bug bug in a different context, so again I think this would need to be opted into. And this would require a way to distinguish the two types of MaybeIncorrect lints programmatically that we currently do not have.