Add warning when comparing a non-optional value to Optional.none

[calda]

This PR ads a warning when comparing a non-optional value to Optional.none.

The compiler already emits a warning when comparing a non-optional value to nil:

let value = "non-optional"

// warning: comparing non-optional value of type 'String' to 'nil' always returns false 
if value == nil {
  print("value is nil")
}

It should also emit a warning when comparing a non-optional value to the Optional.none case:

let value = "non-optional"

// warning: comparing non-optional value of type 'String' to 'Optional.none' always returns false 
if value == .none {
  print("value is nil")
}

// warning: comparing non-optional value of type 'String' to 'Optional.none' always returns false 
if value == Optional.none {
  print("value is nil")
}

// warning: comparing non-optional value of type 'String' to 'Optional.none' always returns false 
if value == String?.none {
  print("value is nil")
}

(In Swift 5.7, these comparisons to nil produce a warning but comparisons to Optional.none do not).

I started a discussion about this on the evolution forums. To me this seems like a bug fix that probably doesn't require an evolution proposal.

[theblixguy]

@swift-ci please smoke test

[theblixguy]

@swift-ci please smoke test

[xedin]

Thank you!

[xedin]

@swift-ci please test