Port asset filters and view options to xplat-editor from Wpf

[xianbaum]

PR Details

Ports the existing Wpf asset filters and view options. Most of the code is identical to the existing Wpf implementation, but some code was changed or refactored due to Avalonia's differences or new language features.

The following view options were not implemented as the required underlying asset explorer is not functionally complete, but will need to be implemented when the asset explorer is ported over.

• "Assets and folders in selected folder". Asset list currently only shows assets, not folders regardless of the option selected.
• View as tiles. Can't be implemented until tile view is implemented
• Zoom in, zoom out. Same reason as above.
• Asset tags seem unimplemented, so tag filters are implemented, but untested as well.

I have not added any unit tests yet, but I can do it if requested. Also, happy to implement any feedback.

Related Issue

#2746

Types of changes

• Docs change / refactoring / dependency upgrade
• 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 change)

Checklist

• My change requires a change to the documentation.
• I have added tests to cover my changes.
• All new and existing tests passed.
• ☑️ I have built and run the editor to try this change out.

[xianbaum]

@dotnet-policy-service agree

[xianbaum]

I just realized there were some files I meant to remove that re-appeared after I tried squashing commits. Fixing now. Fixed!