🏫 Add reviewers and editors to frontmatter

[fwkoch]

This reuses the same stash infrastructure that as funding recipients/investigators.

On the final resolved frontmatter, editors and reviewers are lists of string ids which index into contributors and authors (each of those is still a full object).

(The actual editor/reviewer changes are pretty straightforward frontmatter updates - there was just another related edge case I ironed out to slightly complicate things...)

(This addresses a point in #1009)

[rowanc1]

Worked through the demos locally! Works well. 🚀

[fwkoch]

The changes I made to reduce unnecessary warnings still come up in cases where contributors are defined across project/page, so I'm going to back out those changes before I proceed. I'll just also remove the warning that was appearing about "no given name"