[core:sys/darwin/Foundation] Add bindings for NSPopover and related classes

[JacobEvelyn]

This PR is split into two commits for easier review:

---

[core:sys/darwin/Foundation] Extract NSView bindings to its own file

This commit extracts NSView bindings from NSWindow.odin to a new
NSView.odin file to better match Odin conventions and give us a
better place to add additional NSView bindings in the next commit.

[core:sys/darwin/Foundation] Add bindings for NSPopover and related classes

This commit adds bindings for NSPopover, as well as related classes used
to display the popover and change its content, layout, animation, appearance,
etc.

---

And here's a "minimal" example that showcases much of the functionality working together:

package main

import NS "core:sys/darwin/Foundation"

quit := false

main :: proc() {
	app := NS.Application.sharedApplication()
	app->setActivationPolicy(.Regular)
	app->finishLaunching()
	window := NS.Window.alloc()->initWithContentRect(
		{{500, 500}, {300, 300}},
		{.Closable, .Titled},
		.Buffered,
		NS.NO,
	)
	window->setDelegate(NS.window_delegate_register_and_alloc({
				windowWillClose = proc(_: ^NS.Notification) {
					quit = true
				},
			}, "CustomWindowDelegate", context))
	window->setTitle(NS.MakeConstantString("NSPopover test"))
	window->setIsVisible(true)
	app->activate()

	label := NS.TextField.labelWithString(NS.String.alloc()->initWithOdinString("Hellope"))
	label->setTranslatesAutoresizingMaskIntoConstraints(false) // Required for layout constraints to work

	view := NS.View.alloc()->init()
	view->addSubview(label)
	constraints := [?]^NS.LayoutConstraint {
		label->leadingAnchor()->constraintEqualToAnchorConstant(view->leadingAnchor(), 10),
		label->trailingAnchor()->constraintEqualToAnchorConstant(view->trailingAnchor(), -10),
		label->topAnchor()->constraintEqualToAnchorConstant(view->topAnchor(), 10),
		label->bottomAnchor()->constraintEqualToAnchorConstant(view->bottomAnchor(), -10),
	}
	NS.LayoutConstraint.activateConstraints(
		NS.Array.alloc()->initWithObjects(
			cast([^]^NS.Object)raw_data(constraints[:]),
			len(constraints),
		),
	)

	popover_view_controller := NS.ViewController.alloc()->init()
	popover_view_controller->setView(view)

	popover := NS.Popover.alloc()->init()
	popover->setBehavior(.ApplicationDefined)
	popover->setAppearance(NS.Appearance.appearanceNamed(NS.AppearanceNameAqua))
	popover->setContentViewController(popover_view_controller)
	popover->showRelativeToRect(NS.Rect{{150, 150}, {1, 1}}, window->contentView(), .MaxYEdge)

	for !quit {
		NS.scoped_autoreleasepool()
		event := app->nextEventMatchingMask(
			NS.EventMaskAny,
			NS.Date.distantFuture(),
			NS.DefaultRunLoopMode,
			true,
		)
		for event != nil {
			if event->type() == .LeftMouseDown {
				label->setStringValue(NS.String.alloc()->initWithOdinString("Hellope world!"))

				animation_context := NS.AnimationContext.currentContext()
				animation_context->setAllowsImplicitAnimation(true)
				animation_context->setDuration(1)
				NS.AnimationContext.beginGrouping()
				popover->setContentSize(popover->contentViewController()->view()->fittingSize())
				NS.AnimationContext.endGrouping()
			}
			app->sendEvent(event)
			event = app->nextEventMatchingMask(NS.EventMaskAny, nil, NS.DefaultRunLoopMode, true)
		}
	}
}