- Use the correct absolute path for relative paths within a rooted path
[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.
Use the configuration file path directory as the working directory for the file attribute of the appSettings section instead of the current working directory.
Add tests for AppSettingsSection.
[Jay] Fix memory corruptions: out-of-bounds and uninitialized value.
When dynamically compiling script with a class with a nested class defined, the collection would be null.
Example:
class test
{
 class asd
 {
 }
}
[MWF] Fix opacity of form (#19856)
[MS.Build] add "OS" _undocumented_ predefined property.

It is used by Xamarin.Android to determine which compiler to use (csc or smcs)
and lack of this property simply caused Csc build task failure.