Is your feature request related to a problem? Please describe.
Some external programs such as (neo)vim plugins or termfilechooser rely on giving file managers a path to a file and expecting the cursor to be on that file on startup.

Describe the solution you'd like
When spf is given a path to a file rather than a directory it should open to the parent directory of that file and put the cursor on the given file (if it exists of course).

Current Behavior:
> spf "/a/b/file.txt" -> Opens /a/b/file.txt as a directory, and shows "No such file or directory".

Expected Behavior:
> spf "/a/b/file.txt" -> Opens /a/b as a directory, with file.txt as the file where the cursor is pointing.

Describe alternatives you've considered
None

Additional context
Mentioned in #622, here.

Also briefly brought up in Rolv-Apneseth/tfm.nvim#18.