add force refresh button in navigator

[kpge]

What it does

add a force-refresh button on the toolbar in nagigator as pointed in #5885

How to test

It's hard to test, because file watcher will called fileChanged function, and auto refresh the file tree.
There are two ways to test it:

• First one is check the websocket request in devtools:
  when click force-refresh button, it will send getFileStat request to backend and receive a file node message.
  
• Another way to test :

1. change the value of fs.inotify.max_user_watches to default value(8192) to diable the file wathcer.
   echo fs.inotify.max_user_watches=8192| sudo tee -a /etc/sysctl.conf && sudo sysctl -p
2. start theia app and open a large project (such as theia workspace) in browser.
3. create a new file or folder and click refresh button.
   

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[vzhukovs]

Looks good for me. @kpge thanks for adding this item!

[vince-fugnitto]

Thank you for the contribution @kpge 👍