20 second faster Theia-based workspace startup time

Synced from Eclipse Che issue

https://github.com/eclipse/che/issues/20861

Describe the bug

It takes about 10 sec. after Che-Theia is loaded to the browser and before the project tree is rendered.

Che version

next (development version)

Steps to reproduce

Start a new workspace with the following factory URL:
<che-host>#https://github.com/l0rd/spring&#45;petclinic?devfilePath=.devfilev2.yaml

It takes about 10 sec. before the project tree is rendered. During that time the tree is empty. However, the project sources are already cloned.

Expected behavior

The projects tree should be rendered as soon as Che-Theia page is loaded to the browser.

Runtime

OpenShift

Screenshots

Installation method

OperatorHub

Environment

Linux

Release Notes Text

The previous DevWorkspace based Che-Theia used to take more than 20 seconds to load due to some blocking built-in plugins startup. The built-in plugins are not blocking the main Theia process startup anymore.