Add window user manual resize event callback

This change adds awareness and callback capabilities for window user manual resize (live resize) events to remote_cocoa’s NativeWidgetNSWindowBridge and its related Mojo Host interfaces. For WebView2Mac, if downstream HostingNSWindowBridge inherits from NativeWidgetNSWindowBridge and implements the relevant callbacks (such as for synchronizing window state, optimizing rendering, or interacting with the host application), these new events can be used to achieve more fine-grained window resize responses (for example, pausing/resuming certain operations or optimizing performance when the user drags the window edge). However, this submission does not alter the compatibility of existing interfaces, nor does it remove or modify existing methods, so there is no destructive impact on current WebView2Mac functionality. If downstream does not actively adapt to these new events, there is no direct impact. If downstream wishes to leverage this capability, a better window resize experience can be achieved by overriding the relevant methods.