Restore `lsp-execute-command' as an obsolete defun

Its original function, being a `cl-defgeneric' that can be overriden per
language server is gone; however, PRs were provided to eliminate all
uses of it in that context. To remain backwards-compatible, it will
still remain as an obsolete `defun' that calls `lsp--execute-command'
internally.

Author: nbfalcon

lsp-mode.el

@@ -5169,6 +5169,16 @@ It will show up only if current point has signature help."
       (funcall action-handler action)
     (lsp--send-execute-command command arguments?)))
 
+(defun lsp-execute-command (_ command arguments)
+  "Execute code action COMMAND with ARGUMENTS?.
+Note that this function can now longer be overloaded using
+`cl-defmethod', because that proved to be a liability. Use the
+:action-handlers argument of `make-lsp-client' instead."
+  (lsp--execute-command
+   (lsp-make-command :command (symbol-name command)
+                     :arguments? arguments)))
+(make-obsolete #'lsp-execute-command #'lsp--execute-command "7.1.0")
+
 (lsp-defun lsp-execute-code-action ((action &as &CodeAction :command? :edit?))
   "Execute code action ACTION.
 If ACTION is not set it will be selected from `lsp-code-actions-at-point'."