update to recent JSONSL code

Reverts our clang-format changes (#56402642), our introduction of
bson_malloc / bson_free (#da366bb2), and our change from assert to
BSON_ASSERT (#661e0960). Keep two changes that fix warnings (#a1ca74d8
and #6e0f9c68), which were merged to JSONSL upstream.

Upstream no longer uses "assert()" in the code, although it still
includes assert.h by mistake.

I'll bring bson_malloc / bson_free back in an upcoming commit.