message render: Refactor to group per-message properties too.
message render: Refactor to group per-message properties too.

This refactor is extra simple.  There's no particularly identifiable
semantic meaning to which properties we've put on these three
different types -- they're all just different facts about a given
message -- so collapse that distinction.

This makes the code a bit simpler to read and reason about, and will
also unlock some further useful refactors in this file.

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile