tweak(lsp): lsp-ui-doc-enable = t

This was temporarily disabled due to tremendous slowness on PGTK
clients, which was hopefully addressed in 731ae806e, so we can renable
this.

Fix #5533

modules/tools/lsp/+lsp.el

@@ -196,10 +196,7 @@ instead is more sensible."
         lsp-ui-sideline-show-hover nil
         ;; Re-enable icon scaling (it's disabled by default upstream for Emacs
         ;; 26.x compatibility; see emacs-lsp/lsp-ui#573)
-        lsp-ui-sideline-actions-icon lsp-ui-sideline-actions-icon-default
-        ;; REVIEW Temporarily disabled, due to immense slowness on every
-        ;;        keypress. See emacs-lsp/lsp-ui#613
-        lsp-ui-doc-enable nil)
+        lsp-ui-sideline-actions-icon lsp-ui-sideline-actions-icon-default)
 
   (map! :map lsp-ui-peek-mode-map
         "j"   #'lsp-ui-peek--select-next