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/config.lua

@@ -37,6 +37,7 @@ M.defaults = {
     close = { '<Esc>', 'q' },
     goto_location = '<Cr>',
     peek_location = 'o',
+    restore_location = "<C-g>",
     hover_symbol = '<C-space>',
     toggle_preview = 'K',
     rename_symbol = 'r',