Fix documentation of v1::document::value post-move state

[eramongodb]

Followup to #1412, where the documentation of post-move state for v1::document::value (and v1::array::value via \copydoc) was not correctly updated to account for the default initialization state being changed from "invalid" to "empty", as asserted by the (correctly updated) tests:

mongo-cxx-driver/src/bsoncxx/test/v1/document/value.cpp

Lines 199 to 207 in 91b9c64

	SECTION("move") {
	auto const move = std::move(v);
	CHECK(v.data() == nullptr);
	CHECK_NOFAIL(!v.get_deleter()); // Valid but unspecified state.
	CHECK(move.data() == empty.data());
	CHECK(get_deleter<noop_deleter_type>(move) == noop_deleter);
	}