Create valid xar files

[zorgiepoo]

Create valid xar files by creating file nodes, eg Contents -> Resources -> foo.txt
Before we were just creating all top-level items with paths that had multiple path components, instead of any parent entries, but doing this was wrong.

I also noticed and fixed some incorrect logic determining file equality in creation by the file hash. Now it makes sure the file/symlink contents are equal or they're both directory entires.

This does not break older clients. The applying logic was fortunately written in a way where no changes there are required.
We thus do not need to bump the major version, but we are bumping the minor version of the format here.

I will cherry-pick this change to 1.x once approved / merged.

Fixes #1899

Checklist:

• My change is being tested and reviewed against the Sparkle 2.x branch. New changes must be developed on the 2.x development branch first.
• My change is being backported to master branch (Sparkle 1.x). Please create a separate pull request for 1.x, should it be backported. Note 1.x is feature frozen and is only taking bug fixes, localization updates, and critical OS adoption enhancements.
• I have reviewed and commented my code, particularly in hard-to-understand areas.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• My change is or requires a documentation or localization update

Testing

I tested and verified my change by using one or multiple of these methods:

• Sparkle Test App
• Unit Tests
• My own app
• Other (please specify)

All unit tests pass.
Tested creating and applying new binary delta files between two different versions of an app.
Tested applying a newly generated binary delta file using an older binary delta version works.

Tested both of these combinations on Big Sur and Monterey beta machines.

macOS version tested:
11.5 (20G71)
12.0 Beta (21A5284e)

[ZhuoxingGuo]

Great！ Thank you