This implements the following migration behaviour with older
VLC version:
- Index 0 in settings used to be the Default profile, and is now
  ignored (not read from and not written to anymore)
- The default settings still include the default profile in index
  0, to maintain backwards compatibility if older VLC are started.
- In profile selector, index 0 is still the Default profile,
  if the "apply at next startup" is selected, a new Custom profile
  is created at exit.
- By default after updating, no profile will be deployed at launch,
  so the "Default profile is selected.

refs #19260

(cherry picked from commit 42115489

)
Signed-off-by: David Fuhrmann <dfuhrmann@videolan.org>