fix: apply sizes/srcset when using placeholder

[Kolobok12309]

Fix placeholder working with sizes(srcset)

Bug: After mounting, component load only mainSrc img, ignoring srcset. For mobiles it load full-size image instead of small version, but after loading, same load small version, total it load 3 images: placeholder, fullsize, smallsize

image/src/runtime/components/nuxt-img.ts

Lines 99 to 108 in bc9ddc0

	onMounted(() => {
	if (placeholder.value) {
	const img = new Image()
	img.src = mainSrc.value
	img.onload = () => {
	imgEl.value.src = mainSrc.value
	placeholderLoaded.value = true
	}
	}
	})

#189 (comment)

I don't understand what this piece is for. Mb update before nextTick?

image/src/runtime/components/nuxt-img.ts

Line 104 in bc9ddc0

imgEl.value.src = mainSrc.value

[netlify]

✅ Deploy Preview for nuxt-image ready!

Name	Link
🔨 Latest commit	fff53fa
🔍 Latest deploy log	https://app.netlify.com/sites/nuxt-image/deploys/6480e9273bfdb10008d06784
😎 Deploy Preview	https://deploy-preview-676--nuxt-image.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[danielroe]

Would you be able to add a regression test for this? 🙏

[Kolobok12309]

Would you be able to add a regression test for this? 🙏

Added simple tests for placeholder with src and with sizes