fix(document): avoid treating nested projection as inclusive when applying defaults

[vkarpov15]

Fix #14115

Summary

Right now nested projections, like { prop: { subprop: 1 } }, throw off the logic that checks for projections when applying defaults. So { prop: { subprop: 1 } } will still apply defaults on all properties underneath prop that have defaults other than subprop.

With this PR, we won't treat { prop: { subprop: 1 } } as { prop: 1} for applying defaults, which is what our applyDefaults() function does now.

Examples

[hasezoey]

the code looks good, but any tests for this?

[vkarpov15]

@hasezoey thanks for reminder, I pushed tests in dadac4e