Merge remote-tracking branch 'upstream/features/function-pointers' into function-pointer-type-lookup

* upstream/features/function-pointers: (212 commits)
  Correct public API number.
  Update argument state when parameter has not-null type (#46072)
  Fix TypeWithAnnotations.ToTypeWithState() for (untyped) null literal (#46344)
  Update README (#46136)
  Revert "Revert "Support nullable annotations on unconstrained type parameters""
  Revert "Support nullable annotations on unconstrained type parameters (#45993)"
  Fix type in publish data
  Update VSIXExpInstaller version to one available on ADO
  Update publish data for 16.8
  Update version of RichCodeNav.EnvVarDump
  A fixed initializer must be bound to its natural type (#46293)
  Update features merged into 16.7p4 (#46229)
  Async-streams: disposal should continue without jump within a finally (#46188)
  Recommend default in type constraint, but not record (#46311)
  Add use site diagnostics to IsUnmanaged (#46114)
  Add another flaky test.
  Ensure NuGet connections use TLS 1.2
  Update to Microsoft.CodeAnalysis.Testing 1.0.1-beta1.20374.2
  Skip flaky test.
  Fix build break. (#46303)
  ...