Despite -DENABLE_EXTRA_ALIGNMENT=OFF being a general improvement over our default large alignment specifiers (bson_t aligned at 128 bytes), users still run into issues with the alignment specifiers (e.g. CDRIVER-2880).

It seems tricky to get the alignment specifiers right in all situations. And I'm doubtful that we get any measurable performance improvements by changing alignment.

I think we should:

• Run an experiment (perhaps with our benchmark suite) to see if turning off alignment entirely results in any performance drop.
• If not, let's add a cmake option, like DISABLE_ALIGNMENT that removes alignment specifiers entirely.
• Document that users should configure with this option.