feat: add focus handling to macOS view for proper key event forwarding

[andrewrynhard]

Updated the add_mouse_button_class_method! macro.
Now, when $foc is true, the code calls makeFirstResponder on the window to ensure the view becomes the first responder.
This change enables the plugin view to properly capture keyboard input on macOS.

Credit to @justinfrankel. See #202.

[andrewrynhard]

Fixes #191.

[andrewrynhard]

While we are at it, I believe I am seeing the same issue in Windows. Is that expected? Where would I look if I wanted to fix that?

[kronihias]

This fixes keyboard focus for plugins within Reaper for me (eg. a textfield).

Any chance we can get this merged?

[micahrj]

This is unnecessary. There is already a Window::focus method which calls makeFirstResponder on macOS, which applications can call explicitly e.g. in response to mouse down events:

baseview/src/macos/window.rs

Lines 302 to 310 in 237d323

	pub fn focus(&mut self) {
	unsafe {
	let view = self.inner.ns_view.as_mut().unwrap();
	let window: id = msg_send![view, window];
	if window != nil {
	msg_send![window, makeFirstResponder:view]
	}
	}
	}