cli : support "-" for stdout like stdin (#3050)

cli : support "-" for stdout like stdin (#3050)

This changes examples/cli/cli.cpp to be like
examples/common-whisper.cpp. "-of -" can be specified (or this can be
inferred from "-" as the input file) to output to stdout. This is useful
for piping to other applications.

Log fname_out consistently when not stdout
- Terminals have stdout=stderr, so remove the message before
  successful output to ease copying
- Don't affect actual error messages
- Move opening the ofstream into the factory, fixing missing
  open and/or error messages in output_score/output_wts
- Fix struct naming convention

Closes #3048