fix: wait for theia initalWindow to be set before opening sketch through open-file event

[giacomocusinato]

Motivation

Resolves #2688

Change description

Theia internally create an initial empty window on app start to improve UX while first loading the app instance, see eclipse-theia/theia#12897
On MacOS, since open sketch via file association was triggered before initial window reference was set, the open sketch logic would create a new window instance instead of reusing the early created window reference, leaving an unresponsive additional empty window.

Currently there is no ideal way to wait or react to initialWindow value change, so we pool on the value.
Note that this only needed on the first window startup as on other instances, showWindowEarly is not used and initialWindow is null.
The pool sets a generous amount of retries but should bail consistently on the first try as initialWindow is set right after the app is ready. Note that in case the pools times out, we open the sketch on a new window anyway.