v.builder: enable gc back with msvc, build separate .debug.obj thirdparty files when -g is passed, to prevent linking issues

[spytheman]

• v.pref: enable back the default of -gc boehm for msvc too
• ci: bump msvc-windows job to use windows-2025
• v.builder: switch to using a runtime check for trace_thirdparty_obj_files, to make issue diagnosing easier, by skipping one bootstrapping step
• ci: use -g in VFLAGS too for windows_ci_msvc.yml
• v.builder: use .debug.obj for thirdparty object files, that are build with msvc
• v.builder: fix compilation, use the new .debug.obj files
• ci: restore windows-2022 runner in windows_ci_msvc.yml; remove -g in VFLAGS
• run vfmt