[bugfix] Update GetURL to extract url from Link objects with href (#4249)

# Description

> If this is a code change, please include a summary of what you've coded, and link to the issue(s) it closes/implements.
>
> If this is a documentation change, please briefly describe what you've changed and why.

This pull request updates our parsing of the `url` property in incoming ActivityPub items to also include Link items, and not just bare URIs.

The first discovered url is still used as the *gtsmodel.Account or *gtsmodel.Status `url` property, so this change only really affects our dereference URL anti-spoof check thingy.

~~Should fix https://codeberg.org/superseriousbusiness/gotosocial/issues/4248 but I need to run it and test it myself first to be sure.~~

Fixes https://codeberg.org/superseriousbusiness/gotosocial/issues/4248

## Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: `[ ]` -> `[x]`

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [ ] I/we have made any necessary changes to documentation.
- [x] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4249
Co-authored-by: tobi <tobi.smethurst@protonmail.com>
Co-committed-by: tobi <tobi.smethurst@protonmail.com>

internal/ap/extract.go

@@ -357,10 +357,14 @@ func ExtractIconURI(i WithIcon) (*url.URL, error) {
 			continue
 		}
 
-		imageURL, err := ExtractURL(image)
-		if err == nil && imageURL != nil {
-			return imageURL, nil
+		imageURL := GetURL(image)
+		if len(imageURL) == 0 {
+			// Nothing here.
+			continue
 		}
+
+		// Got a hit.
+		return imageURL[0], nil
 	}
 
 	return nil, gtserror.New("could not extract valid image URI from icon")
@@ -399,10 +403,14 @@ func ExtractImageURI(i WithImage) (*url.URL, error) {
 			continue
 		}
 
-		imageURL, err := ExtractURL(image)
-		if err == nil && imageURL != nil {
-			return imageURL, nil
+		imageURL := GetURL(image)
+		if len(imageURL) == 0 {
+			// Nothing here.
+			continue
 		}
+
+		// Got a hit.
+		return imageURL[0], nil
 	}
 
 	return nil, gtserror.New("could not extract valid image URI from image")
@@ -488,28 +496,6 @@ func ExtractFields(i WithAttachment) []*gtsmodel.Field {
 	return fields
 }
 
-// ExtractURL extracts the first URI it can find from the
-// given WithURL interface, or an error if no URL was set.
-// The ID of a type will not work, this function wants a URI
-// specifically.
-func ExtractURL(i WithURL) (*url.URL, error) {
-	urlProp := i.GetActivityStreamsUrl()
-	if urlProp == nil {
-		return nil, gtserror.New("url property was nil")
-	}
-
-	for iter := urlProp.Begin(); iter != urlProp.End(); iter = iter.Next() {
-		if !iter.IsIRI() {
-			continue
-		}
-
-		// Found it.
-		return iter.GetIRI(), nil
-	}
-
-	return nil, gtserror.New("no valid URL property found")
-}
-
 // ExtractPubKeyFromActor extracts the public key, public key ID, and public
 // key owner ID from an interface, or an error if something goes wrong.
 func ExtractPubKeyFromActor(i WithPublicKey) (
@@ -676,15 +662,15 @@ func ExtractAttachments(i WithAttachment) ([]*gtsmodel.MediaAttachment, error) {
 // (just remote URL, description, and blurhash) from the given
 // Attachmentable interface, or an error if no remote URL is set.
 func ExtractAttachment(i Attachmentable) (*gtsmodel.MediaAttachment, error) {
-	// Get the URL for the attachment file.
+	// Get the first URL for the attachment file.
 	// If no URL is set, we can't do anything.
-	remoteURL, err := ExtractURL(i)
-	if err != nil {
-		return nil, gtserror.Newf("error extracting attachment URL: %w", err)
+	remoteURL := GetURL(i)
+	if len(remoteURL) == 0 {
+		return nil, gtserror.New("empty attachment URL")
 	}
 
 	return &gtsmodel.MediaAttachment{
-		RemoteURL:   remoteURL.String(),
+		RemoteURL:   remoteURL[0].String(),
 		Description: ExtractDescription(i),
 		Blurhash:    ExtractBlurhash(i),
 		FileMeta: gtsmodel.FileMeta{