[Feature]: Get rid of sheetDismisser and use environment

[tmolitor-stud-tu]

Precondition

• I understood that this template is only for feature requests and not for bug reports

Cross-checked related issues?

• I have cross-checked this overview Overview: Tasks and Issues #322 as well as filtered for related labels https://github.com/monal-im/Monal/labels

Describe your feature

Don't use our own sheetDismisser but @Environment(\.presentationMode) var presentationMode and presentationMode.wrappedValue.dismiss() instead. Should even be valid on iOS 14.

[tmolitor-stud-tu]

Only cases still present in code are dismisses without animation, there seems no appropriate replacement (yet) in swiftui.