MacPDF: Make clicking outline items have an effect

Clicking an item in the outline now opens that page.

This requires giving the outline view a delegate, which for some
reason also has th effect of indenting expandable items ¯\_(ツ)_/¯
The vertical alignment of text still looks off, though.

Meta/Lagom/Contrib/MacPDF/MacPDFWindowController.h

@@ -15,7 +15,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 @class MacPDFDocument;
 
-@interface MacPDFWindowController : NSWindowController <MacPDFViewDelegate, NSToolbarDelegate>
+@interface MacPDFWindowController : NSWindowController <MacPDFViewDelegate, NSOutlineViewDelegate, NSToolbarDelegate>
 
 - (instancetype)initWithDocument:(MacPDFDocument*)document;
 - (IBAction)showGoToPageDialog:(id)sender;

Meta/Lagom/Contrib/MacPDF/MacPDFWindowController.mm

@@ -116,6 +116,7 @@
     // FIXME: Only set data source when sidebar is open.
     _outlineDataSource = [[MacPDFOutlineViewDataSource alloc] initWithOutline:_pdfDocument.pdf->outline()];
     _outlineView.dataSource = _outlineDataSource;
+    _outlineView.delegate = self;
 }
 
 - (IBAction)showGoToPageDialog:(id)sender
@@ -175,4 +176,17 @@
     return nil;
 }
 
+#pragma mark - NSOutlineViewDelegate
+
+- (void)outlineViewSelectionDidChange:(NSNotification*)notification
+{
+    NSInteger row = _outlineView.selectedRow;
+    if (row == -1)
+        return;
+
+    OutlineItemWrapper* item = [_outlineView itemAtRow:row];
+    if (auto page = [item page]; page.has_value())
+        [_pdfView goToPage:page.value()];
+}
+
 @end