help: Fix printing list of wrap mode
help: Fix printing list of wrap mode

Implement a string converter in our WrapMode enum so that argparse will
only print the names in the doc instead of WrapMode.<name>.

This changes --help command from printing:
  --wrap-mode {WrapMode.default,WrapMode.nofallback,WrapMode.nodownload,WrapMode.forcefallback}
to:
  --wrap-mode {default,nofallback,nodownload,forcefallback}

Fixes issue #4067

jpakkane/meson,jpakkane/meson,jpakkane/meson,QuLogic/meson,QuLogic/meson,MathieuDuponchelle/meson,jeandet/meson,pexip/meson,pexip/meson,jpakkane/meson,mesonbuild/meson,jpakkane/meson,jeandet/meson,becm/meson,QuLogic/meson,pexip/meson,pexip/meson,pexip/meson,mesonbuild/meson,jeandet/meson,jeandet/meson,pexip/meson,QuLogic/meson,MathieuDuponchelle/meson,mesonbuild/meson,becm/meson,jpakkane/meson,becm/meson,MathieuDuponchelle/meson,MathieuDuponchelle/meson,becm/meson,jeandet/meson,pexip/meson,becm/meson,jeandet/meson,jpakkane/meson,QuLogic/meson,mesonbuild/meson,QuLogic/meson,mesonbuild/meson,MathieuDuponchelle/meson,becm/meson,becm/meson,QuLogic/meson,QuLogic/meson,mesonbuild/meson,jpakkane/meson,mesonbuild/meson,becm/meson,mesonbuild/meson,pexip/meson,MathieuDuponchelle/meson,MathieuDuponchelle/meson,jpakkane/meson,jeandet/meson,jeandet/meson,jeandet/meson,pexip/meson,MathieuDuponchelle/meson,mesonbuild/meson,becm/meson,MathieuDuponchelle/meson,becm/meson,mesonbuild/meson,QuLogic/meson,pexip/meson