feat: Add follow_cursor and restore_location

New lua API function: follow_cursor (supports opts.focus_outline).
This sets location in outline to match location in code.

New keymap: restore_location (C-g) by default.
This provides the same functionality as follow_cursor.

I've also refactored other lua API functions for consistency of using
`opts.focus_outline`. If opts is not provided, focus_outline is
defaulted to true. To change this behaviour, set it to false.

lua/symbols-outline/providers/coc.lua

@@ -83,11 +83,12 @@ local function convert_symbols(result)
 end
 
 ---@param on_symbols function
-function M.request_symbols(on_symbols)
+---@param opts table
+function M.request_symbols(on_symbols, opts)
   vim.fn.call('CocActionAsync', {
     'documentSymbols',
     function(_, symbols)
-      on_symbols { [1000000] = { result = convert_symbols(symbols) } }
+      on_symbols({ [1000000] = { result = convert_symbols(symbols) } }, opts)
     end,
   })
 end