feat: show keymaps for builtin actions (#1084)

* Add default mappings `<C-/>`and `?` for insert and normal mode, respectively, to show registered keymappings (`actions.which_key`) attached to prompt buffer

lua/telescope/mappings.lua

@@ -30,6 +30,7 @@ mappings.default_mappings = config.values.default_mappings
       ["<C-q>"] = actions.send_to_qflist + actions.open_qflist,
       ["<M-q>"] = actions.send_selected_to_qflist + actions.open_qflist,
       ["<C-l>"] = actions.complete_tag,
+      ["<C-_>"] = actions.which_key, -- keys from pressing <C-/>
     },
 
     n = {
@@ -56,6 +57,7 @@ mappings.default_mappings = config.values.default_mappings
 
       ["<C-u>"] = actions.preview_scrolling_up,
       ["<C-d>"] = actions.preview_scrolling_down,
+      ["?"] = actions.which_key,
     },
   }
 
@@ -222,6 +224,7 @@ mappings.execute_keymap = function(prompt_bufnr, keymap_identifier)
   assert(key_func, string.format("Unsure of how we got this failure: %s %s", prompt_bufnr, keymap_identifier))
 
   key_func(prompt_bufnr)
+  vim.cmd [[ doautocmd User TelescopeKeymap ]]
 end
 
 mappings.clear = function(prompt_bufnr)