feat(lua): replace buffer with buf in vim.keymap.set/del #38360

The `buffer` option remains functional but is now undocumented.
Providing both will raise an error. Since providing `buf` was disallowed
before, there is no code that will break due to using `buffer` alongside
`buf`.

runtime/scripts/optwin.lua

@@ -701,9 +701,9 @@ else
       local name = line:match('[^\t]*')
       vim.cmd.help(("'%s'"):format(name))
     end
-  end, { buffer = buf })
+  end, { buf = buf })
 
-  vim.keymap.set({ 'n', 'i' }, '<space>', update_current_line, { buffer = buf })
+  vim.keymap.set({ 'n', 'i' }, '<space>', update_current_line, { buf = buf })
 end
 
 vim.cmd '1'