[feat] Allow creation of child Window for macOS

[Hupka]

Describe the problem

It is possible to "bind" two windows as parent & child in most operating systems. By doing so, they share additional behavior which is currently not possible to replicate with Tauri.

Right now, the solution is partially implemented in Tauri and Tao. When looking through the Git history, it seems like maybe it was "forgotten" to extend support to at least include macOS.

Describe the solution you'd like

In May 2021, the feature to model a parent/child relationship between windows was added for Windows OS.

• Link to Tauri API
• Link to feature request ticket

In August 2021, the same feature for macOS was included in tao. The PR owner was so kind even to include a working example that showcases the desired behavior.

• Link to Tao PR
• Link to example implementation

Desired solution: Include tao functionality for parent/child relation into Tauri the same way as it already is for Windows.