[Feat] Allow for multiple dialogs with dialog manager

[KThompson-Lane-Unity]

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Description of new feature

Currently the dialog manager only supports a single dialog being shown at any one time. It would be really useful to allow for multiple to be shown at once, overlaying on one another allowing for you to return to the state of a previous dialog after closing the top-most one. For example the dialog manager could contain a stack of 'active' dialogs which could be accessed allowing for individual dismissal / showing / hiding of dialogs.

This would be very useful for cases where you would like to show a message to the user while still wanting the previously open dialogs to show afterwards without having to add confusing event handling logic.

Package Version

6.0.0-rc