feat(lsp): add client command support to codelens (#15820)

Also adds a check against the server capabilities to fix
https://github.com/neovim/neovim/issues/15183

test/functional/plugin/lsp/codelens_spec.lua

@@ -58,5 +58,33 @@ describe('vim.lsp.codelens', function()
     ]], bufnr)
 
     eq({[1] = {'Lens1', 'LspCodeLens'}}, virtual_text_chunks)
+
+  end)
+  it('codelens uses client commands', function()
+    local fake_uri = "file:///fake/uri"
+    local cmd = exec_lua([[
+      fake_uri = ...
+      local bufnr = vim.uri_to_bufnr(fake_uri)
+      vim.fn.bufload(bufnr)
+      vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, {'One line'})
+      local lenses = {
+        {
+          range = {
+            start = { line = 0, character = 0, },
+            ['end'] = { line = 0, character = 8 }
+          },
+          command = { title = 'Lens1', command = 'Dummy' }
+        },
+      }
+      vim.lsp.codelens.on_codelens(nil, lenses, {method='textDocument/codeLens', client_id=1, bufnr=bufnr})
+      local cmd_called = nil
+      vim.lsp.commands['Dummy'] = function(command)
+        cmd_called = command
+      end
+      vim.api.nvim_set_current_buf(bufnr)
+      vim.lsp.codelens.run()
+      return cmd_called
+    ]], fake_uri)
+    eq({ command = 'Dummy', title = 'Lens1' }, cmd)
   end)
 end)