Improve responsiveness of loading a document into Form Editor

In a large project, loading a *.ui.qml file into the Form Editor can take a long time.

A customer reported that it can take ~20s to load one form, or ~5s to load a Washing Machine example form. Their hardware specs are:

• OS: Windows 10
• RAM: 32 GB
• CPU: Intel Core i7-8750H (12 cores), ~2.2GHz
• GPU: NVIDIA Quadro P2000

Furthermore:

• During the loading period (after double-clicking the QML file but before the form appears on-screen), Qt Design Studio is unresponsive.
• The load delay occurs each time the form is opened, even within the same session. When switching back and forth between 2 forms, the same delay occurs with each switch.

Suggestions

• Use asynchronous loading, so that Qt Design Studio does not freeze while waiting for the load to complete.
• Implement some form of project caching to speed up the loading of *.ui.qml files.