fix(csharp_ls): use the correct language id #4298

In [recent commit](https://github.com/razzmatazz/csharp-language-server/commit/f51cd9dec8b10b7fd8f475dac3a904e1da2c7217),
`csharp-language-server` started checking the language id due to the
support of Razor documents. Since vim's file type for C# is `cs` so all
things like hover documentation, go-to-definition etc. stopped working
after this commit when using the default config. This PR fixes that by
adding `get_language_id` to `csharp_ls.lua`.

1 files changed, 6 insertions, 0 deletions

diff --git a/lsp/csharp_ls.lua b/lsp/csharp_ls.lua
index dd8c427a..e284090b 100644
--- a/lsp/csharp_ls.lua
+++ b/lsp/csharp_ls.lua
@@ -29,4 +29,10 @@ return {
   init_options = {
     AutomaticWorkspaceInit = true,
   },
+  get_language_id = function(_, ft)
+    if ft == 'cs' then
+      return 'csharp'
+    end
+    return ft
+  end,
 }