Support importing/exporting XML files

[isc-bsaviano]

This PR fixes #1158

See the docs for how to use the new commands.

[isc-bsaviano]

@gjsjohnmurray @daimor This can be tested with the latest 2023.2 developer preview kit.

[isc-bsaviano]

@daimor @gjsjohnmurray Can you please test this when you have some time? I would like to get this and a few other changes merged so we can do a 2.10.0 release soon.

[gjsjohnmurray]

I've done a little bit of testing made a couple of comments. I also noticed that the Import command pre-populates the "File name" field of the Windows File Open dialog with the string "de-workspace", as though it's grabbing the last 12 characters of the XYZ.code-workspace file I'd saved my ISFS workspace into.

[isc-bsaviano]

I've done a little bit of testing made a couple of comments. I also noticed that the Import command pre-populates the "File name" field of the Windows File Open dialog with the string "de-workspace", as though it's grabbing the last 12 characters of the XYZ.code-workspace file I'd saved my ISFS workspace into.

The grabbing of the last 12 characters might be a VS Code bug, but I use the workspace file's URI as the default for the file picker because otherwise it will show be a virtual file picker for your isfs workspace folder. I want to ensure that it always opens a file picker using the local file system.

[gjsjohnmurray]

When running this VSIX build in VS Code debug I was able to solve weird the Import dialog field prepopulation by dropping the filename from the path of the defaultUri. I have proposed a change.