Accept URLs when optimizing site icons

[crazytonyli]

Description

Change path: String to url: URL, to avoid any potential URL parsing issues. This will save use some URL -> String -> URL conversions, since the current callers pass URL.absoluteString as the path.

It'll prevent a potential issue where a scheme-less URL string is passed as path, because URL(string: "i.wp.com/icon.png").host is nil.

[dangermattic]

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[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress by scanning the QR code below to install the corresponding build.

	App Name	WordPress
	Configuration	Release-Alpha
	Build Number	33605
	Version	PR #25868
	Bundle ID	org.wordpress.alpha
	Commit	433e972
	Installation URL	5f4v35n9ej080

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[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack by scanning the QR code below to install the corresponding build.

	App Name	Jetpack
	Configuration	Release-Alpha
	Build Number	33605
	Version	PR #25868
	Bundle ID	com.jetpack.alpha
	Commit	433e972
	Installation URL	2jv5bqt5rhppg

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.