Add workspaceFolders/configuration/window to 3.15

[reznikmm]

It seems workspaceFolders and configuration properties were lost, but they are present in 3.14.
The window property is new in 3.15, let's add it to ClientCapabilities definition

[msftclas]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

❌ reznikmm sign now
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[dbaeumer]

Thanks again ! Merged by hand due to conflicts.

You might want to think about signing the CLA if you plan to provide more PRs.