Make redundant_discardable_let and unused_optional_binding opt-in

[klaaspieter]

I believe code should be as easy possible to change. I think redundant_discardable_let and unused_optional_binding make code harder to change. Because of this I would prefer them to be opt-in rules.

They make code harder to change because with redundant_discardable_let the let has to be prepended again when the requirements change such that the value does have to be captured.

The unused_optional_binding is even harder because the code has to change from a trailing != nil to a leading let name =.

These rules are debated in the community and I think they should therefore be an opt-in rule

[freak4pc]

+1 on this. Attaching the original Unused Optional Binding discussion with @jpsim and @marcelofabri as a followup.

I am still in favor of perhaps finding a more thorough method of determining if a rule should be implemented as opt-in. I also agree with @marcelofabri that we should aim having most rules as default and be opinionated as other linters, but those opinions should be backed by a community standard or some sort of a majority, and not just by a portion of developers IMO.

[idrougge]

I agree that this rule is not established well enough in the Swift community as preferable (many would say that if let _ = is more idiomatic Swift) to warrant being enabled by default.

[stale]

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