Revert "remove obsolete dijitBorderContainerNoGutter and dijitBorderContainerNoGutterPane classes, refs #17966"
Turns out they weren't obsolete after all.
See the "gutters=false" example in test_BorderContainer.html and notice
the padding just inside the BorderContainer's border.

This reverts commit adfcd3bd30fae997a8cb8a3891b8c5aa324f1c76.
Fixes #18097.
Remove debugging console.log() from, fixes #18120.
It snuck into the code in 333e91c3a622eb8e123bb1bcf04494df610a22ad.
Clarify doc about BorderContainer.design vs. a child's layoutPriority.
Fixes #18138.