Fix Cmd+plus zoom handling on non-US layouts (#680)

Sources/KeyboardLayout.swift

@@ -11,4 +11,36 @@ class KeyboardLayout {
 
         return nil
     }
+
+    /// Translate a physical keyCode to the unmodified character under the current keyboard layout.
+    static func character(forKeyCode keyCode: UInt16) -> String? {
+        guard let source = TISCopyCurrentKeyboardInputSource()?.takeRetainedValue(),
+              let layoutDataPointer = TISGetInputSourceProperty(source, kTISPropertyUnicodeKeyLayoutData) else {
+            return nil
+        }
+
+        let layoutData = unsafeBitCast(layoutDataPointer, to: CFData.self)
+        guard let bytes = CFDataGetBytePtr(layoutData) else { return nil }
+        let keyboardLayout = UnsafeRawPointer(bytes).assumingMemoryBound(to: UCKeyboardLayout.self)
+
+        var deadKeyState: UInt32 = 0
+        var chars = [UniChar](repeating: 0, count: 4)
+        var length = 0
+
+        let status = UCKeyTranslate(
+            keyboardLayout,
+            keyCode,
+            UInt16(kUCKeyActionDisplay),
+            0,
+            UInt32(LMGetKbdType()),
+            UInt32(kUCKeyTranslateNoDeadKeysBit),
+            &deadKeyState,
+            chars.count,
+            &length,
+            &chars
+        )
+
+        guard status == noErr, length > 0 else { return nil }
+        return String(utf16CodeUnits: chars, count: length).lowercased()
+    }
 }