Experimental SSR plugin

[developit]

This adds support for wmr.config.js, and uses it in the demo app to demonstrate an SSR middleware.

ToDo:

• have the SSR plugin use the same prerender() export we support for prod prerendering
• filter out verbose node module loader logs
• production SSR (maybe this is too different of a case?)

[JoviDeCroock]

Looks great! Should we convert this into a monorepo'ish structure to have some plugins that we offer (also as an inspiration to people who want to implement their own)?

[developit]

Possibly - they have to be published independently of the main package, but that doesn't seem like a huge issue. In the case of this SSR thing I'm not sure if it's ready to be a proper plugin, was more of a way to keep the experiment working without landing it in core.

[github-actions]

Size Change: -41 B (0%)

Total Size: 693 kB

Filename	Size	Change
demo/dist/about/index.html	635 B	-1 B
demo/dist/chunks/compat.********.js	14.9 kB	+1 B
demo/dist/chunks/index.********.js	210 B	-106 B (50%)	🏆
demo/dist/compat/index.html	1.53 kB	-1 B
demo/dist/env/index.html	691 B	-1 B
demo/dist/index.html	681 B	-1 B
wmr.cjs	662 kB	+68 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
demo/dist/assets/Calendar.********.css	702 B	0 B
demo/dist/assets/style.********.css	386 B	0 B
demo/dist/chunks/class-fields.********.js	207 B	0 B
demo/dist/chunks/prerender.********.js	2.45 kB	0 B
demo/dist/class-fields/index.html	612 B	0 B
demo/dist/error/index.html	622 B	0 B
demo/dist/files/index.html	654 B	0 B
demo/dist/index.********.js	6.89 kB	0 B

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[JoviDeCroock]

Should we revive this into a custom plugin? Do we expect a production server running, if so will we have output targets that make it easy to publish i.e. person wants a serverless way to serve it or a normal deploy on a server?

[Inviz]

I have an idea for project where I'd need to SSR some pages on demand, and currently I'm on the fence if I should go with preact/wmr for it... I'd really love to, but I wish there was a decent way to do it without doing crazy hacks. Don't wanna go with Rails :)

Not sure if it's useful but here's a +1 for this feature