[websocket] Implement HttpListenerContext.AcceptWebSocketAsync().
[websocket] Cleaner closing.
[websocket] Better hijacking.
[websocket] Use string.Equals instead of String.Compare
[websocket] Don't use string +=
Reimplement StreamWebSocket.
Fix some bugs.
Support CloseStatus
Support receiving frame larger than buffer.
Use do ... while (true)
Fix handling fragment and opcode.
Fix indent of author.
Remove checking Origin header.

RFC requires Origin header for browser client.
Non browser client may be omit Origin header.
[Jay] Fix memory corruptions: out-of-bounds and uninitialized value.
[corlib] Add Guid hex format parsing with whitespaces. Fixes #19915
[System.Core][ios] Fix value for ENAMETOOLONG (typo?) internal constant in System.IO.MemoryMappedFiles.MemoryMappedFile
[llvm] Update to the llvm backend to work with llvm a82b09c3a3efbfaf2ce39adc113f9a5458cde398.
[corlib] Fix public api
Merge pull request #981 from methane/websocket

[websocket] Implement HttpListenerContext.AcceptWebSocketAsync()
[runtime] Clean up an #ifdef block.