[Perf] [Check] High Allocator DoWriteIfNeeded

[benaadams]

Items 2 & 3 on highest allocators in plaintext test

Microsoft.AspNet.Server.Kestrel.Http.SocketOutput.WriteContext

Allocations

Writes alloc on List.Add not GCHandle.Alloc for clarity

Bytes

Writes alloc on List.Add not GCHandle.Alloc for clarity

Further up the stack...

DoPostWork is burning 346,416 bytes in calling the Action<object, object> CallbackAdapter method (the byte difference in the method) though I'm not entirely sure why?

[benaadams]

Added PR for the closure in DoWriteIfNeeded; doesn't resolve everything though but should clean up 461888 bytes from the last line.

[benaadams]

Redoing post closure cleanup