feat(orgbrowser): add support for StandardValueSet

[mohanraj-r]

What does this PR do?

Builds the community contribution #3982 from @sbresin 🎉

Adds support for retrieving StandardValueSet Metadata with the Org Browser.

There is no API call that lists all StandardValueSets, so i hardcoded the list of their names. The list comes from here: https://developer.salesforce.com/docs/atlas.en-us.api_meta.meta/api_meta/standardvalueset_names.htm

What issues does this PR fix or reference?

#1579

Functionality Before

None: Currently it is not possible at all to retrieve StandardValueSets from the OrgBrowser.

Functionality After

[uip-robot-zz]

This issue has been linked to a new work item: W-10936512

[klewis-sfdc]

Looks great to me! Thanks for the contribution @sbresin!

✅ Org Browser Retrieve Source works for StandardValueSets
✅ Org Browser Retrieve Source and Open works for StandardValueSets
✅ Org Browser Retrieve Source for all Standard Value Sets via directory-level retrieve button works
✅ Adding a new picklist option to a standard value set and then re-running Retrieve Source via Org Browser to retrieve the new value works (also works via right click on file in Explorer)
✅ Adding a new picklist option to a standard value set and then running SFDX: Diff file against org works and shows correct diff