Fix type definition of `TheiaAppFactory`

[tortmayr]

What it does

Ensure that the TheiaAppFactory type does match the constructor function of TheiaApp. InitialWorkspace is required in the TheiaApp constructor butwas optional in TheiaAppFactory This ensures that (sub)classes of TheiaApp can properly be used as app factory without type casting

Contributed on behalf of STMicroelectronics

How to test

Using the TheiaAppLoader with a TheiApp (sub)class as factory parameter should now work and not have a ts error:

// Mock playwright args
cons args= {} as TheiaPlaywrightTestConfig & PlaywrightWorkerArgs

// Simle test 
const app= TheiaAppLoader.load({playwright,browser}, undefined, TheiaApp)

// test with subclass
class SpecialTheiaApp extends TheiaApp{
}
const app:SpecialTheiaApp= TheiaAppLoader.load({playwright,browser}, undefined, SpecialTheiaApp)

On master this would throw a compile error and a cast like `SpecialTheiaApp as TheiaAppFactory<SpecialApp>` would required

Follow-ups

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