AppKit: Let an editable text view take the Tab key

CPWindow handled every Tab key press itself and moved to the next key view, so a text view never received Tab and could not insert a tab character.

It now follows Cocoa: an editable text view takes plain Tab and inserts a tab, while Control-Tab, Shift-Tab and Tab in other views still move through the key view loop.

* CPResponder.j: Add _wantsTabKey, which returns NO by default.

* CPTextView/CPTextView.j: Want the Tab key while editable.

* CPWindow/CPWindow.j: Pass plain Tab to a first responder that wants it, and keep the browser from moving its own focus.

AppKit/CPResponder.j

@@ -290,6 +290,16 @@ CPDeleteForwardKeyCode  = 46;
 {
 }
 
+/*
+    @ignore
+    Returns YES if the receiver handles the Tab key itself, as an editable text view does by
+    inserting a tab character. Otherwise the window uses Tab to move to the next key view.
+*/
+- (BOOL)_wantsTabKey
+{
+    return NO;
+}
+
 - (void)insertBackTab:(id)sender
 {
 }

AppKit/CPTextView/CPTextView.j

@@ -1839,6 +1839,16 @@ Sets the selection to a range of characters in response to user action.
     [self insertText:@"\t"];
 }
 
+/*
+    @ignore
+    As in Cocoa, an editable text view takes the Tab key and inserts a tab character.
+    Control-Tab still moves to the next key view.
+*/
+- (BOOL)_wantsTabKey
+{
+    return [self isEditable];
+}
+
 - (void)insertTabIgnoringFieldEditor:(id)sender
 {
     [self insertTab:sender];

AppKit/CPWindow/CPWindow.j

@@ -2007,8 +2007,14 @@ CPTexturedBackgroundWindowMask
             return [[self firstResponder] keyUp:anEvent];
 
         case CPKeyDown:
+            // Tab moves to the next key view, unless the first responder takes plain Tab itself, as an
+            // editable text view does to insert a tab character. Control-Tab always moves on, as in Cocoa.
+            var modifierFlags = [anEvent modifierFlags],
+                firstResponderTakesTab = !(modifierFlags & (CPShiftKeyMask | CPControlKeyMask)) && [[self firstResponder] _wantsTabKey];
+
             if ([anEvent charactersIgnoringModifiers] === CPTabCharacter &&
-                !([anEvent modifierFlags] & (CPAlternateKeyMask | CPCommandKeyMask)))
+                !(modifierFlags & (CPAlternateKeyMask | CPCommandKeyMask)) &&
+                !firstResponderTakesTab)
             {
                 if ([anEvent modifierFlags] & CPShiftKeyMask)
                     [self selectPreviousKeyView:self];
@@ -2044,6 +2050,10 @@ CPTexturedBackgroundWindowMask
                 return;
             }
 
+            // A first responder that takes Tab gets the key, and the browser must not also move its own focus.
+            if (firstResponderTakesTab && [anEvent charactersIgnoringModifiers] === CPTabCharacter && CPDOMAvailable)
+                [[[anEvent window] platformWindow] _propagateCurrentDOMEvent:NO];
+
             [[self firstResponder] keyDown:anEvent];
 
             // Trigger the default button if needed