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.
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