Move ManagedHandler version/chunking validation earlier

[stephentoub]

Move it to ManagedHandler.SendAsync rather than HttpConnection.SendAsync so that it happens before we even try to get a connection. A minor benefit of the change as well is that isHttp10 is no longer lifted to the state machine.

Fixes https://github.com/dotnet/corefx/issues/26709
cc: @geoffkizer, @pjanotti

[geoffkizer]

LGTM

[stephentoub]

@dotnet/dnceng, FYI:
https://ci3.dot.net/job/dotnet_corefx/job/master/job/windows-TGroup_netcoreapp+CGroup_Release+AGroup_x86+TestOuter_false_prtest/7830/

D:\j\workspace\windows-TGrou---f8ac6754\Tools\CloudTest.Helix.targets(216,5): warning : An error occurred while sending the request. [D:\j\workspace\windows-TGrou---f8ac6754\src\upload-tests.proj]
D:\j\workspace\windows-TGrou---f8ac6754\Tools\CloudTest.Helix.targets(216,5): warning :    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) [D:\j\workspace\windows-TGrou---f8ac6754\src\upload-tests.proj]
D:\j\workspace\windows-TGrou---f8ac6754\Tools\CloudTest.Helix.targets(216,5): warning :    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) [D:\j\workspace\windows-TGrou---f8ac6754\src\upload-tests.proj]
D:\j\workspace\windows-TGrou---f8ac6754\Tools\CloudTest.Helix.targets(216,5): warning :    at Microsoft.DotNet.Build.CloudTestTasks.AzureHelper.<RequestWithRetry>d__13.MoveNext() [D:\j\workspace\windows-TGrou---f8ac6754\src\upload-tests.proj]

@dotnet-bot test Windows x86 Release Build please