fix(assets): make srcset parsing HTML spec compliant (#16323)

[rarous]

fixes #16323

Description

Simplifies the spitting of srcset image candidates with descriptors, so it is compliant with spec and not driven by every edge case somebody finds out is not working.

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[sapphi-red]

Thanks!

[rarous]

HMR tests on Node 22 are a bit brittle :-/ The failure is unrelated to my changes and possible race condition/context leaking. I got another error on my machine just in the first run of tests. All consecutive runs were ok.

 FAIL  playground/hmr/__tests__/hmr.spec.ts > soft invalidate
AssertionError: expected 'soft-invalidation/index.js is transfo…' to match 'soft-invalidation/index.js is transfo…'

Expected: "soft-invalidation/index.js is transformed 2 times. child is now updated?"
Received: "soft-invalidation/index.js is transformed 3 times. child is now updated?"

[patak-dev]

Nice!