[navigator] add refresh command and toolbar item

[tetchel]

The theia new-folder detection does not appear to be perfect - see eclipse-archived/codewind#67. I'd like to be able to manually refresh the Explorer from my extension.

In VS Code, I see the command workbench.files.action.refreshFilesExplorer. I suppose there should be an equivalent command in Theia, but perhaps there isn't yet because there is no refresh button in the Explorer view like there is in VS Code:

Currently we have to refresh the browser tab, which is not really an acceptable work around.

[akosyakov]

It is up to grab. One can add a refresh command and toolbar item first, and then add workbench.files.action.refreshFilesExplorer command to the plugin system which delegates to the navigator command. It could be 2 separate PRs.

[vince-fugnitto]

Closed in #5885

[akosyakov]

@kpge @vince-fugnitto We need to register workbench.files.action.refreshFilesExplore in the plugin system which delegates to navigator.refresh.