Allow to switch to folder/workspace without window reload

[isidorn]

#34774

1. VSCode, open a no folder vscode
2. Click on the big open folder button in the explorer
3. Notice that VSCode reloads - unlike most other scenarios where we are adding aditional folders where this just happens

[bpasero]

This scenario is blocked by not being able to start/stop extensions without window reload. The folder to open could have specific extension settings configured.

[sandy081]

We have two blockers for this

• Changing UI state (UI State: introduce and adopt event to be able to change UI state dynamically #35123)
• Extensions

If we tackle the UI state issue we are good to go for 90 percent of cases. Having different extensions per workspace is less likely. We can trigger reload in only such cases.

[bpasero]

Backlog:

• understand the consequences of entering an existing workspace without reload (memory, processes, singlestons, etc.)
  • limit this only to transitions from an empty workspace into a workspace?
• restore workspace associated state (e.g. the opened editors)
• restore backups

[sandy081]

With individual APIs to stop & start extension hosts, we can now restart extension host with new set of extensions ie., those which are enabled for the folder that is getting opened.