Add support for new C# language server (lsp-roslyn) (#4279) #5260

Job	Run time
test (ubuntu-latest, 27.2, false)	2m 2s
test (ubuntu-latest, 28.2, false)	2m 25s
test (ubuntu-latest, 29.3, false)	2m 22s
test (macos-latest, 28.2, false)	3m 28s
test (macos-latest, 29.3, false)	4m 3s
test (windows-latest, 27.2, false)	2m 34s
test (windows-latest, 28.2, false)	3m 18s
test (windows-latest, 29.3, false)	2m 57s
test (ubuntu-latest, snapshot, true)	1m 30s
test (macos-latest, snapshot, true)	2m 36s
test (windows-latest, snapshot, true)	1m 8s
	28m 23s

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