[Source Tooling] Refactoring action to convert if statement to switch

[Regno]

Implement action to convert if statements from:

var e = E.case1
if e == .case1 {}
else if e == .case2 {}
else {}

to

  var e = E.case1
  switch e {
  case .case1: break
  case .case2: break
  default: break
  }

Resolves SR-5740.

P.S. I can't reopen previous PR](#26719) because of force push to branch after rebase. I remade refactoring action to resolve comments from previous PR.

@nathawes please take a look to new implementation.

[nathawes]

This looks great! Thanks for all the improvements. Just left one suggestion to improve the tests, but I'm happy to merge this without it too.

[nathawes]

It'd be good to type check the output file for each of these to make sure the code we're generating is valid and continues to type check as the compiler changes. You can do that be adding an extra RUN line like the below:

// RUN: %target-swift-frontend-typecheck %t.result/L9-3.swift

[Regno]

Added for each test case.

[nathawes]

@swift-ci please test

[nathawes]

@swift-ci Please Sourcekit Stress test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 904bd0b

[nathawes]

Looks like a few of the existing tests need updating to allow for the new refactoring kind being in the list:

/Users/buildnode/jenkins/workspace/swift-PR-osx/branch-master/swift/test/refactoring/RefactoringKind/basic.swift:431:30: error: CHECK-EXTRCT-METHOD-NEXT: is not on the line after the previous match
// CHECK-EXTRCT-METHOD-NEXT: Action ends
                             ^
<stdin>:4:1: note: 'next' match was here
Action ends
^
<stdin>:2:15: note: previous match ended here
Extract Method
              ^
<stdin>:3:1: note: non-matching line after previous match is here
Convert To Switch Statement

[Regno]

Tests are failed at cases like this:

if a {
    return
  } else {
    return
  }

I think there are no sense to convert if statement with single bool condition to switch statement. So I just skip such kind of if at isApplicable function. Now all tests should be passed.

[nathawes]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 904bd0b

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 904bd0b