Profile Config: inconsistent parsing of `print/start_gcode` vs `filament/start_filament_gcode`

Description of the bug

While working on a custom python parsing and building of config.ini profile files, a bug is discovered: when encoding multi-line custom gcode commands, there is an inconsistent parsing and encoding of the print/start_gcode vs the filament/start_filament_gcode, namely, in the PrusaSlicer cpp code base:

start_filament_gcode uses quotes "bracketing" depending on single-vs-multi line commands
while start_gcode can not use quotes "bracketing" regardless of single-vs multi line commands

The bug manifests itself as following in the UI, when selecting a custom config.ini in the preset list:

trying to use start_gcode with quotes results in unusable gcode entry
trying to use start_filament_gcode without quotes results in empty gcode entries
and no errors are reported in either case

The bug can also be confirmed by a basic config file search in the repository: file search for start_gcode = vs file search for start_filament_gcode =

This bug also affects other similar custom gcode config entries.

This issue is a request to:

make config.ini parsing and encoding consistent
report errors in the UI when incoming user files errors are wrong

Project file & How to reproduce

N/A

Checklist of files included above

[ ] Project file
[ ] Screenshot

Version of PrusaSlicer

Version 2.7.4+linux-x64-GTK3

Operating system

Linux work3 6.7.9-arch1-1 #1 SMP PREEMPT_DYNAMIC Fri, 08 Mar 2024 01:59:01 +0000 x86_64 GNU/Linux

Printer model

N/A

prusa3d / PrusaSlicer