Moved OakCreateActionPopUpButton method to OakUIConstructionFunctions.h

While code reuse is an added benefit, the main motivation was to fix the appearance of the action popup button in the Find window. The first (placeholder) item in the Find window's action button was assigned a nop action so that when the button was clicked and it's menu validated, the "action" image would always appear as disabled.
Limit clipboard history display string to ~1024 code points

This should fix performance issues (during scroll).
Exclude divider images from accessibility

Since it is the cell that is providing the accessibility attributes the simplest way I could think of to have it ignored was to remove NSImageView’s support for the NSAccessibilityChildrenAttribute.

I tried using accessibilitySetOverrideValue:forAttribute: but it did not work for me, so a subclass was required.
Delete unused code
Improve alignment of glob text field in find window

The combo box’s top border should now align with the pop-up buttons on the same line, though it’s not baseline aligned.
Only set raised background style for borderless action buttons
Set accessibility description when creating action buttons
Use view’s undo manager rather than the window’s
Use undo manager’s menu item titles in file browser action menu
Use local undo manager for file browser

This ensures that ⌘Z / ⇧⌘Z are only targeting the file browser when it has focus.

Previously these keys would act on the file browser undo stack when a view without it’s own undo/redo stack had focus, e.g. HTML output view.