Split "executable" from "its arguments" in blender & ffmpeg commands.
Use `{blenderArgs}` variable to hold the default Blender arguments,
instead of having both the executable and its arguments in `{blender}`.
The reason for this is to support backslashes in the Blender executable
path. These were interpreted as escape characters by the shell lexer.
The shell lexer based splitting is now only performed on the default
arguments, with the result that `C:\Program Files\Blender
Foundation\3.3\blender.exe` is now a valid value for `{blender}`.
This does mean that this is backward incompatible change, and that it
requires setting up Flamenco Manager again, and that older jobs will not
be able to be rerun.
It is recommended to remove `flamenco-manager.yaml`, restart Flamenco
Manager, and reconfigure via the setup assistant.
Fix the FFmpeg unit test on Windows, by:
- Having actual input files (otherwise the input-glob-creation-function
errors out), and
- ensuring the cleanup function is always run, and
- testing for the right CLI arguments.
