refactor(swingset-runner): Convert RESM to NESM

[kriskowal]

Refs #527

This change removes the ESM emulation layer in favor of standing directly on Node.js’s ESM implementation. A second commit adds a coverage script (with no enforced thresholds).

[kriskowal]

Lint won’t pass until I cut a new release of @endo/eslint-config. The demo directory entrains dependencies but should only entrain devDependencies.

[FUDCo]

LGTM. It's always great when somebody else does the remarkably tedious parts.

[kriskowal]

It's always great when somebody else does the remarkably tedious parts.

It’s a living, but in fairness, git grep __dirname | cut -d: -f1 | xargs -o vim did most of the work.