Spins the Slint event loop and returns a promise that resolves when the loop terminates.
If the event loop is already running, then this function returns the same promise as from the earlier invocation.
Optional
As Function it defines a callback that's invoked once when the event loop is running.
Spins the Slint event loop and returns a promise that resolves when the loop terminates.
If the event loop is already running, then this function returns the same promise as from the earlier invocation.