chore: Make JSDom a peer/dev dependency on NodeJS only

[gonfunko]

The basics

• I validated my changes

The details

Resolves

Fixes #8775

Proposed Changes

This PR removes JSDom as a normal dependency, and adds the latest version as a peer and dev dependency. It also uses the browser field in package.json to indicate to bundlers and the like that it should be omitted for builds targeting a browser, rather than Node-based, deployment environment.

[BenHenning]

Thanks @gonfunko! The change looks reasonable, though perhaps we may need to drop the version upgrade for now. Left one comment on that per the failing CI.

Edit: Also, it's very cool that the new package.json now implies Blockly has zero dependencies (though it's hard to be sure without scanning the package lock file).

[BenHenning]

Gemini thinks the upgraded version here is likely causing the build failures since this was part of the CI logs:

2026-01-22T00:00:56.5787404Z npm warn EBADENGINE Unsupported engine {
2026-01-22T00:00:56.5787981Z npm warn EBADENGINE   package: 'jsdom@27.4.0',
2026-01-22T00:00:56.5788484Z npm warn EBADENGINE   required: { node: '^20.19.0 || ^22.12.0 || >=24.0.0' },
2026-01-22T00:00:56.5788980Z npm warn EBADENGINE   current: { node: 'v18.20.8', npm: '10.8.2' }
2026-01-22T00:00:56.5789308Z npm warn EBADENGINE }

(I was curious but didn't actually want to debug).

Can we avoid the version upgrade for now?

[gonfunko]

I think we actually just want to drop the old Node versions for v13, but we should have a team chat about how aggressive to be about that.