Fix bug: Shift modifier incorrectly added to filter shortcuts

[svobs]

• I have read CONTRIBUTING.md
• This implements/fixes issue Saved filter key shortcuts: lowercase letters have shift modifier added #3998.

---

Description:
See above issue for problem description.

Summary / conclusions
This terrifying block of code appears to be the culprit:

extension NSEvent {
  var readableKeyDescription: (String, String) {
    get {

      let rawKeyCharacter: String
      if let char = NSEventKeyCodeMapping[Int(self.keyCode)] {
        rawKeyCharacter = char
      } else {
        let inputSource = TISCopyCurrentASCIICapableKeyboardLayoutInputSource().takeUnretainedValue()
        if let layoutData = TISGetInputSourceProperty(inputSource, kTISPropertyUnicodeKeyLayoutData) {
          let dataRef = unsafeBitCast(layoutData, to: CFData.self)
          let keyLayout = unsafeBitCast(CFDataGetBytePtr(dataRef), to: UnsafePointer<UCKeyboardLayout>.self)
          var deadKeyState = UInt32(0)
          let maxLength = 4
          var actualLength = 0
          var actualString = [UniChar](repeating: 0, count: maxLength)
          let error = UCKeyTranslate(keyLayout,
                                     UInt16(self.keyCode),
                                     UInt16(kUCKeyActionDisplay),
                                     UInt32((0 >> 8) & 0xFF),
                                     UInt32(LMGetKbdType()),
                                     OptionBits(kUCKeyTranslateNoDeadKeysBit),
                                     &deadKeyState,
                                     maxLength,
                                     &actualLength,
                                     &actualString)
          if error == 0 {
            rawKeyCharacter = String(utf16CodeUnits: &actualString, count: maxLength).uppercased()

          } else {
            rawKeyCharacter = KeyCodeHelper.keyMap[self.keyCode]?.0 ?? ""
          }
        } else {
          rawKeyCharacter = KeyCodeHelper.keyMap[self.keyCode]?.0 ?? ""
        }
      }

      return (([(.control, "⌃"), (.option, "⌥"), (.shift, "⇧"), (.command, "⌘")] as [(NSEvent.ModifierFlags, String)])
        .map { self.modifierFlags.contains($0.0) ? $0.1 : "" }
        .joined()
        .appending(rawKeyCharacter), rawKeyCharacter)
    }
  }
}

The value it returns will always be in uppercase, which is fine for display purposes, but it shouldn't have been using it to store the "raw" key value (The code was already grabbing the raw value from the user and putting it in currentKey, and it was far simpler to just use that). It has another problem: it seems to add 3 null characters to the string it returns. The debugger shows that t is stored as T\0\0\0.

This is not good, but I'm going to punt and declare it to be outside the scope of this defect.

After this fix, readableKeyDescription is only used in two places:

1. In FilterWindowController for display. At least this doesn't seem to be breaking anything.
2. In KeyCodeHelper.mpvKeyCode(), where it is checked for inequality against another string, causing a block of code to always evaluate to true - which is ok because that block should always be executed.

This should be cleaned up at some point. Rather than try to debug that block, a more prudent solution would be to remove all use of it and find a simpler substitute if needed. At least this PR makes strides in that direction.

[low-batt]

Reproduced problem. Pulled PR locally, built, confirmed it fixed the problem.

[uiryuu]

Thanks!