Allow serverForUri to return password for unnamed server (#837)

[gjsjohnmurray]

This PR fixes #837

@isc-bsaviano please use the dev VSIX to verify that this meets the need without exposing passwords that may have come from Server Manager's authentication provider.

[gjsjohnmurray]

@isc-bsaviano sorry, there's no dev VSIX until #839 gets approved by @daimor and added to this branch.

[gjsjohnmurray]

@isc-bsaviano the CI for the prerelease branch is now in place and has built a dev vsix at https://github.com/intersystems-community/vscode-objectscript/suites/5069595553/artifacts/150724470

Please install it manually (e.g. by dropping it onto the Extensions view) and test it meets the need identified in #837 without exposing passwords in other situations.

Be aware that it won't show as a pre-release in the Extensions view in the way it would if installed from Marketplace (see microsoft/vscode#140949 (comment) for why). To prove it was packaged using the --pre-release switch you can rename the vsix to have a .zip extension, look inside it, examine the extension.vsixmanifest file, and confirm the presence of this:

<Property Id="Microsoft.VisualStudio.Code.PreRelease" Value="true" />