Refactor to use TryFrom

[hawkw]

Since the TryFrom trait is in unstable Rust (rust-lang/rust#33417), we should rewrite a lot of failable conversions into TryFrom implementations. For example, a lot of the ELF parsing code that returns Result<Self, ElfError> can probably be rewritten to use TryFrom.

Where removing existing failable conversion methods would break a lot of other code, we can temporarily preserve the existing API by having it wrap a try_from call, and phase it out gradually.

We don't have to worry about TryFrom not being on stable, since we can't build SOS on stable anyway.

[hawkw]

I'm marking this as "easy" since it is a reasonably simple refactoring that doesn't require a great deal of OS knowledge.

[tirkarthi]

As an update to the issue the above RFC was implemented and merged with PR : rust-lang/rust#49305 . It caused notable breakages in the ecosystem and got reverted : rust-lang/rust#49518

[hawkw]

@tirkarthi my understanding is that all that was reverted is the addition of TryFrom to the prelude, the traits are still stabilized, correct?

[tirkarthi]

Yes, the team is looking for a way to introduce this with less breakages.