Problem: Changing `src` of an existing plugin cleanly requires manual
`vim.pack.del()` prior to executing `vim.pack.add()` with a new `src`.
Solution: Autodetect `src` change for an existing plugin (by comparing
against lockfile data). If different - properly delete immediately and
treat this as new plugin installation.
Alternative solution might be to update `origin` remote in the
installed plugin after calling `vim.pack.update()`. Although, doable,
this 1) requires more code; and 2) works only for Git plugins (which
might be not the only type of plugins in the future). Automatic
"delete and clean install" feels more robust.
2e533e364e