Fixes #60005

Introduces the concept of a re-trigger character to the signature help provider. This is a seperate set of characters that are registered with the provider. Typing a retrigger character fires a new signature help request if signature help is already showing.

#54972

Fixes #53466

Fixes #59151

* make actionbar support different trigger keys

* add some undefined checks

Dispose of webviews after each test run

Added actions from #57321 to the 'No Settings Found'-message

Multiple repls per debug session

The previous solution involved an own solution with an array of
disposables. The new solution makes use of the _register-method from the
Displosable class.