Rule Request: avoid if-not-else

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

Rule Request

1. Proposal: when an if statement includes the else clause, the if clause should not be negated. The same applies to the ternary operator.

2. Examples:

// Would trigger:
  if !test {
    methodA()
  } else {
    methodB()
  }

  if !(testA || testB) {
    methodA()
  } else {
    methodB()
  }

  !test ? methodA() : methodB()

// Would not trigger:
  if test {
    methodB()
  } else {
    methodA()
  }

  if testA || testB {
    methodB()
  } else {
    methodA()
  }

  if test ? methodB() : methodA()

3. Should the rule be configurable, if so what parameters should be configurable?
   Not that I can think of.

4. Should the rule be opt-in or enabled by default? Why?
   I, personally, would say yes, as if one is handling both possibilities, there is no need to do it with inverted logic.

Locate SwiftLint's existing rule entry points and corresponding rule tests, then compare how conditional and ternary expressions are handled. Verify completion against the listed triggering and non-triggering examples, including negated if statements, negated compound conditions, and ternary expressions.