SERVER-10159 Reuse damage vector across object updates
SERVER-10159 Inline Element::OK and Document::end; they are called often
SERVER-10159 Elements never have null Document pointers
SERVER-10159 Don't acquire rep just to check type when resolving
SERVER-10159 Always obtain BSONElement field names as StringData
SERVER-10159 Retain concatenated dotted path and return it that way when possible.
SERVER-10159 Expand universe of types eligible for in-place update

Eligibility criteria are that type be a leaf type, non-deprecated, carries payload data (e.g
not null or undefined), and is not structurally complex (e.g. code with scope), and has some
likelihood of sharing layout.