[Feature Request] Add diffed image attachment support for swift-testing

[Kyle-Ye]

Describe the bug

https://forums.swift.org/t/pitch-image-attachments-in-swift-testing/80867

swift-testing will add image attachment support soon.

Use the issue to track attachment support for swift-testing in this framework

Expected behavior

Show the diffed image attachment in Xcode or diffed image in console.

Additional context

swift-snapshot-testing/Sources/SnapshotTesting/AssertSnapshot.swift

Lines 458 to 470 in b198a56

	if !attachments.isEmpty {
	#if !os(Linux) && !os(Android) && !os(Windows)
	if ProcessInfo.processInfo.environment.keys.contains("__XCODE_BUILT_PRODUCTS_DIR_PATHS"),
	!isSwiftTesting
	{
	XCTContext.runActivity(named: "Attached Failure Diff") { activity in
	attachments.forEach {
	activity.add($0)
	}
	}
	}
	#endif
	}

[amaurydavid]

A branch was created for that right after the WWDC. There's more work to do as it doesn't compile right now, but it shows they are working on it.