Add unstable support for an Extensible Events room version (`org.matrix.msc1767.10`) via [MSC1767](https://github.com/matrix-org/matrix-spec-proposals/pull/1767), [MSC3931](https://github.com/matrix-org/matrix-spec-proposals/pull/3931), [MSC3932](https://github.com/matrix-org/matrix-spec-proposals/pull/3932), and [MSC3933](https://github.com/matrix-org/matrix-spec-proposals/pull/3933).