V17/image upload mapper

[KevinJump]

Splits the imageCropper and ImageUploadMapper into two different mappers.

• previously we handled these two controls as one, because the image cropper could contain the same structure (a simple string) as the image upload.
• but in reality the image cropper should be a JSON string, and the upload is just a string.
• normalize string media paths into JSON croppers for consistancy. #812 fixed cropper inconsistencies (turned the string into JSON) but this causes problems for the image upload.
• rather than code a condition we have separated the mappers and given them a shared base,
• this resolved the issue now and keeps the code clean

[Copilot]

Pull request overview

This PR separates image cropper and image upload value mapping so croppers continue to use JSON cropper payloads while upload fields remain plain strings.

Changes:

• Introduces a shared ImagePathMapperBase for media path rewriting and dependency discovery.
• Narrows ImagePathMapper to image cropper editors and adds ImageUploadMapper for upload fields.
• Updates block JSON expansion behavior and bumps selected Umbraco package versions/schema outputs.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
uSync.Core/Mapping/Mappers/ImagePathMapperBase.cs	Adds shared media path and dependency handling for image-related mappers.
uSync.Core/Mapping/Mappers/ImagePathMapper.cs	Refactors cropper mapper to inherit shared logic and only target image cropper editors.
uSync.Core/Mapping/Mappers/ImageUploadMapper.cs	Adds upload-field mapper that preserves plain string upload paths.
uSync.Core/Mapping/SyncBlockMapperBase.cs	Expands nested JSON strings during import property conversion.
Directory.Packages.props	Bumps selected Umbraco package versions.
uSync.Tests/packages.lock.json	Updates requested Umbraco.Cms version in the test lock file.
uSync.Tests/appsettings-schema.json	Regenerates schema text with escaped Unicode sequences.

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