feat(builtin.buffers): enhance and bind delete_buffer action (#3145)

* feat(builtin.buffers): enhance and bind `delete_buffer` action

* change default bind and add docs

* [docgen] Update doc/telescope.txt
skip-checks: true

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Co-authored-by: Github Actions <actions@github>

lua/telescope/pickers.lua

@@ -535,6 +535,7 @@ function Picker:find()
   self.__original_mousemoveevent = vim.o.mousemoveevent
   vim.o.mousemoveevent = true
 
+  self.original_bufnr = a.nvim_get_current_buf()
   self.original_win_id = a.nvim_get_current_win()
   _, self.original_cword = pcall(vim.fn.expand, "<cword>")
   _, self.original_cWORD = pcall(vim.fn.expand, "<cWORD>")