Tracking .NET 8 and 9 updates

[m-redding]

• Add a .NET 8 target to RequiredTargetFrameworks and implicitly remove dependencies for packages built into the runtime in .NET 6 and beyond
  • Pull Request:
    • [Experiment] .NET 8 #46637
  • Related:
    • [QUERY] Dependencies mayhem #38857
    • [BUG] Azure sdk references packages that live in the .NET 6+ ref and runtime packs. #28477
    • Added explicit .NET 6 TFMs. #28911
    • Consider adding explicit net6.0 targetFramework outputs for all clients #28492
    • [Core] Investigate implications of adding explicit net6.0 targets for all clients #28577
    • [FEATURE REQ] Remove unnecessary package references for net 6+ TFM #41628
• Add .NET 9 to the test matrix and remove .NET 6
• Update BCL packages to 8.x if possible
  • Check PowerShell compatibility
  • Check Functions compatibility - .NET 8 in-proc host?
  • Related:
    • Update System.Memory.Data to 8.0.0 #46280
• Update global.json to .NET 9
• Condition Microsoft.AspNetCore.Mvc.Testing in Packages.Data.Props #45426
• Modernize Azure.Core targets, net461 doesn't work with some of the 8.x dependencies. Should the net6.0 target be removed?