feat(specifications): render a list in simplified mode

[LeoMcA]

It would've taken a whole lot of repetition (or overhead plumbing) to DRY render and renderSimplified here, so I've added a new simplifiedMode property which can be used instead.

This also gives us the flexibility to turn simplifiedMode into an enum in the future to specify different simplified targets, imagine something like:

renderSimplified() {
  switch(this.simplifiedMode) {
    case "mcp":
        return ...
    case "standalone-zip":
        return ...
    case "carrier-pigeon":
        return ...

[github-actions]

207dbc6 was deployed to: https://fred-pr1504.review.mdn.allizom.net/

[caugner]

LGTM, just one nit.

PS: If we document simplifiedMode somewhere, we could mention this (alternative) strategy.

[caugner]

nit: Could we make this an if (this.simplifiedMode) { return html…; } block instead? Even though it's obvious, I had to look twice to see which branch is which.