Use URI object when invoking vscode.open

[vinistock]

Motivation

While adding jump to view on the Rails addon Shopify/ruby-lsp-rails#412, I noticed a few issues with the openUris implementation.

Implementation

1. The vscode.open command expects a URI object, not a string
2. We didn't have a title for the quick pick so the list of files just showed up with no explanation
3. I added go to file icons to further communicate that selecting an option will jump to it
4. The full URI is way too long to display as label. Started using only the file name