Brush up vertical rhythm of form-check in docs. Closes #25546
Brush up vertical rhythm of form-check in docs. Closes #25546

This adds `form-group` to add the same vertical space to the `form-check` as in other grouped controls
used in form sample markup.

Thanks!

inway/bootstrap,GerHobbelt/bootstrap,gijsbotje/bootstrap,Hemphill/bootstrap-docs,nice-fungal/bootstrap,yuyokk/bootstrap,zalog/bootstrap,fschumann1211/bootstrap,bardiharborow/bootstrap,joblocal/bootstrap,fschumann1211/bootstrap,m5o/bootstrap,stanwmusic/bootstrap,fschumann1211/bootstrap,creativewebjp/bootstrap,creativewebjp/bootstrap,seanwu99/bootstrap,GerHobbelt/bootstrap,bardiharborow/bootstrap,GerHobbelt/bootstrap,bardiharborow/bootstrap,m5o/bootstrap,bootstrapbrasil/bootstrap,tagliala/bootstrap,creativewebjp/bootstrap,tjkohli/bootstrap,Lyricalz/bootstrap,yuyokk/bootstrap,fschumann1211/bootstrap,seanwu99/bootstrap,nice-fungal/bootstrap,gijsbotje/bootstrap,zalog/bootstrap,joblocal/bootstrap,kvlsrg/bootstrap,joblocal/bootstrap,nice-fungal/bootstrap,twbs/bootstrap,stanwmusic/bootstrap,Hemphill/bootstrap-docs,tagliala/bootstrap,bootstrapbrasil/bootstrap,peterblazejewicz/bootstrap,Lyricalz/bootstrap,Hemphill/bootstrap-docs,seanwu99/bootstrap,bootstrapbrasil/bootstrap,seanwu99/bootstrap,stanwmusic/bootstrap,peterblazejewicz/bootstrap,tagliala/bootstrap,yuyokk/bootstrap,tjkohli/bootstrap,yuyokk/bootstrap,creativewebjp/bootstrap,Hemphill/bootstrap-docs,twbs/bootstrap,gijsbotje/bootstrap,inway/bootstrap,kvlsrg/bootstrap,stanwmusic/bootstrap,joblocal/bootstrap,inway/bootstrap,kvlsrg/bootstrap,coliff/bootstrap,Lyricalz/bootstrap,gijsbotje/bootstrap,coliff/bootstrap,zalog/bootstrap,peterblazejewicz/bootstrap,Lyricalz/bootstrap,bardiharborow/bootstrap