Code Quality: Migrate DllImportAttribute to LibraryImportAttribute at NativeFindStorageItemHelper.cs

[gumbarros]

Resolved / Related Issues

• Were these changes approved in an issue or discussion with the project maintainers? In order to prevent extra work, feature requests and changes to the codebase must be approved before the pull request will be reviewed. This prevents extra work for the contributors and maintainers.
  Part of Code Quality: Replace Vanara with CsWin32 #15000
  Validation
  How did you test these changes?
• Did you build the app and test your changes?
• Did you check for accessibility? You can use Accessibility Insights for this.
• Did you remove any strings from the en-us resource file?
  • Did you search the solution to see if the string is still being used?
• Did you implement any design changes to an existing feature?
  • Was this change approved?
• Are there any other steps that were used to validate these changes? No

Screenshots (optional)
Add screenshots here.

[gumbarros]

Need help with someone with Win32 knowledge to know if this CharSet property is important, the only equivalent is StringMarshalling

[gumbarros]

This PR is broken because LibraryImportAttribute requires custom marshaling for custom structs and I don't have deep knowledge of low level programming :(