plugin: add support for refreshFilesExplorer

[vince-fugnitto]

What it does

Fixes: #5885.

The commit adds support for the workbench.files.action.refreshFilesExplorer command on the plugin side
which delegates to the REFRESH_NAVIGATOR command.

How to test

1. add vscode-refresh-explorer test plugin.
2. on master the execution of the test: refresh explorer command will throw an error on the backend.

root ERROR [hosted-plugin: 21091] With stack trace: Error: Command with id 'workbench.files.action.refreshFilesExplorer' is not registered.
    at CommandRegistryMainImpl.<anonymous> (file:///home/evinfug/workspaces/theia/examples/electron/lib/packages_plugin-ext_lib_hosted_browser_hosted-plugin_js.bundle.js:3228:35)
    at step (file:///home/evinfug/workspaces/theia/examples/electron/lib/packages_plugin-ext_lib_hosted_browser_hosted-plugin_js.bundle.js:3138:23)
    at Object.next (file:///home/evinfug/workspaces/theia/examples/electron/lib/packages_plugin-ext_lib_hosted_browser_hosted-plugin_js.bundle.js:3119:53)
    at file:///home/evinfug/workspaces/theia/examples/electron/lib/packages_plugin-ext_lib_hosted_browser_hosted-plugin_js.bundle.js:3113:71
    at new Promise (<anonymous>)

3. on the pull-request the execution of the test: refresh explorer command will successfully execute.

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

Signed-off-by: vince-fugnitto vincent.fugnitto@ericsson.com

[msujew]

I can confirm that the issue exists on master and is addressed by this change nicely.