[Examples] Fix build time getting progressively slower

[kungfooman]

Fixes #5872

Before we had watchers in examples/rollup.config.js that would simply copy build outputs over into /dist/:

    { src: '../build/playcanvas.d.ts', dest: 'dist/playcanvas.d.ts' },
    { src: '../build/playcanvas.js', dest: 'dist/iframe/playcanvas.js' },
    { src: '../build/playcanvas.dbg.js', dest: 'dist/iframe/playcanvas.dbg.js' },
    { src: '../build/playcanvas.prf.js', dest: 'dist/iframe/playcanvas.prf.js' },
    { src: '../build/playcanvas-extras.js', dest: 'dist/iframe/playcanvas-extras.js' },

This worked nice with running npm run develop and if you spawn another shell with target=debug_es5 npm run watch it keeps working for a while aswell, but over time it does more and more, the two rollup processes get in some kind of "create / watch - do stuff / create do stuff again" loop or something.

This can be fixed when we stop putting watchers on build outputs and instead use the rollup target configuration functions (e.g. function buildTarget(buildType, moduleFormat)) directly in examples/rollup.config.js for building the mentioned build outputs.

This is not complicated by itself, but what makes the PR a bit bigger is the separation of a few functions that we need to call from the Examples rollup script.

I confirm I have read the contributing guidelines and signed the Contributor License Agreement.

[mvaligursky]

Nice one @kungfooman , much appreciated. The separation into modules is great!
I'll merge this now and give it a good test over the next few days as I work on some new engine features.

[mvaligursky]

So far this has worked great, no issues .. and maybe even fixed another issue, where sometimes changes from extras were ignored and I have to manually build extras to get those in again.

[kungfooman]

So far this has worked great, no issues .. and maybe even fixed another issue, where sometimes changes from extras were ignored and I have to manually build extras to get those in again.

🙏 Thank you for testing! It's always hard to tell side effects here and there, so I was prepared that some other issue would suddenly pop up again (Whac-A-Mole 😅)