fix(document): avoid massive perf degradation when saving new doc with 10 level deep subdocs

[vkarpov15]

Fix #14897

Summary

Saving a new doc with many very deep subdocs is extremely expensive: the test case in this PR fails after 35 seconds on my local without the change I made to lib/document.js. Saving a new doc 10 levels deep is still more expensive than I'd like, this test now takes maybe 300ms, I'll investigate why this is so slow and add a benchmark.

Examples

[hasezoey]

Looks good, will this be in the next minor version for caution?

[vkarpov15]

I don't think it is necessary to put this change in a minor release. As far as I can tell, there's no observable difference with the changes in this PR other than perf improvements. Subdoc middleware and getters will still get called normally, this PR just removes a bunch of work.

[vkarpov15]

No meaningful change on insertManySimple benchmark. But createDeepNestedDocArray benchmark difference is massive: 223ms vs 34802ms on master on 10 level deep subdocs. Over 100x speedup 😎