Lint TryFrom with infalliable error type

[clarfonthey]

Implementations of TryFrom should always have a falliable error type; instead, infalliable conversions should be implemented via From with the blanket conversion.

[oli-obk]

It should be enough to check for ? operators or anything creating a Result other than Ok(foo)

[0xazure]

I'm interested in having a go at implementing this lint, just want to make sure it's still up for grabs.

[Ralith]

@rustbot claim

[ComputerDruid]

@rustbot claim

(taking this over from @Ralith )