CDRIVER-4363 add client bulk write (#1590)

* fix comment in `_mongoc_write_opmsg`

This is a drive-by fix to fix the referenced payload numbers.

* quote key in match error

* propagate error for numeric mismatch

Otherwise, if the type mismatches, the test runner aborts with an error: "expected int64, int32, or double [...]" that does not identify the field.

* add `ASSERT_EQUAL_BSON`

To do exact BSON matches

* align print on match failure

To ease reading error message

* implement client bulk write

include some tests of basic usage and libmongoc-specific behavior. Specification and prose tests test driver-agnostic behavior.

* add example use

* add prose tests

* add specification tests

* support string `w` URI option in test runner

To support `w=majority`

* update unified test runner

* add `BSON_OPTIONAL_PARAM` macro

* replace `BSON_ASSERT (X || true)` with `BSON_OPTIONAL_PARAM (X)`