Added 'explorerExclude.showPicker' configuration option, which when f…

[rw3iss]

…alse will NOT show the file picker, but only hide the currently selected item

What's this PR do?

It adds a check in util.js for a configuration/setting option: "explorerExclude.showPicker".
If this is true (or undefined), the extension works as is... if it is false it will NOT show any file picker/choose after clicking 'Add to hidden items...', but will only hide the already selected item.

Where should the reviewer start?

util.js line 383

How should this be manually tested?

Add a vscode setting called: "explorerExclude.showPicker": false and then try to hide any selected item. Set the value to true and confirm the default behavior works.

Any background context you want to provide?

Sure - I was glad to find an extension that would work within Workspaces, as the 'Make Hidden' extension doesn't. Upon using this, I simply want to hide one item at a time in the explorer (main use case), quickly, without being prompted every time, so I thought making this a configuration option made sense.

Definition of Done:

• [ x] You have actually run this locally and can verify it works
• You have verified that npm test passes without issue
• [ x] You have updated the README file (if appropriate)

[rw3iss]

Seems to be an issue with folders not being hideable... I'm not sure if this is by design (from vscode or anywhere), but will omit for now, unless you can amend to allow folders to be hideable.