feat(lsp): add support for completionItem.command resolving

`command` was already resolved via a `completionItem/resolve` request
but only if `additionalTextEdits` were also present, and the
`resolveSupport` capability wasn't listed.

Closes https://github.com/neovim/neovim/issues/32406

runtime/lua/vim/lsp/protocol.lua

@@ -458,6 +458,7 @@ function protocol.make_client_capabilities()
           resolveSupport = {
             properties = {
               'additionalTextEdits',
+              'command',
             },
           },
           tagSupport = {