Fix disclosure button being outside its superview bounds. Issue 12729

The centerX constraint on the label was pushing the disclosure button
outside the view's leading edge, making it barely clickable.

Author: gnachman

sources/iTermDisclosableView.m

@@ -170,9 +170,9 @@ - (instancetype)initWithFrame:(NSRect)frameRect prompt:(NSString *)prompt messag
             [self addSubview:_textView];
         }
 
+        [_disclosureButton.leadingAnchor constraintEqualToAnchor:self.leadingAnchor].active = YES;
         [_disclosureButton.centerYAnchor constraintEqualToAnchor:_labelField.centerYAnchor].active = YES;
         [_labelField.leadingAnchor constraintEqualToAnchor:_disclosureButton.trailingAnchor constant:4].active = YES;
-        [_labelField.centerXAnchor constraintEqualToAnchor:self.centerXAnchor].active = YES;
         [_labelField.topAnchor constraintEqualToAnchor:self.topAnchor].active = YES;
         if (_scrollView) {
             [_scrollView.leadingAnchor constraintEqualToAnchor:self.leadingAnchor constant:8].active = YES;