types: avoid inferring Boolean, Buffer, ObjectId as Date in schema definitions under certain circumstances

[vkarpov15]

Fix #14630

Summary

#14630 pointed out that, under certain circumstances that I'm unable to quantify exactly, Boolean, mongoose.Schema.Types.ObjectId, and several other schema types get inferred as dates. This doesn't happen in tsd, or if Mongoose is symlinked into node_modules, so we can't write tests for this issue with our current testing setup.

I tracked the issue down to somehow typeof NativeDate catching Boolean and other data class types. This PR appears to fix the issue, and doesn't break any existing code that we're currently aware of.

Examples