Summary of Changes

Similar to #16259 this creates a service factory for use with creating objects in the Toolbar API. This should make things a little more flexible as it relates to creating new objects and creating custom objects if needed in extensions.

Testing Instructions

Fundamentally, this is the same as #16259 for testing. The CMS by default should continue to function without error, for those looking for advanced integrations they can create and inject new logic.

Documentation Changes Required

• As of 5.0, when a Toolbar object is created a factory must be passed into the constructor; for ease of migration with 4.0 this won't be a required argument
• Typehint and document the correct Toolbar object in the ToolbarButton constructor, this breaks B/C if anyone were trying something like new StandardButton(new stdClass); but since the class internals would break without a Toolbar instance and the number of places where one should be direct instantiating a ToolbarButton should be minimal (if at all) so it should be a low risk change