Almost all functions in the Windows API that open or create objects and return HANDLEs to them return null on failure; only a few (mostly to do with the file system) return INVALID_HANDLE_VALUE on failure. This PR scrubs the repo of a few, but not necessarily all, cases where INVALID_HANDLE_VALUE was mistakenly used or tested against instead of null. In particular, it fixes 2 cases reported in issue #427 where the return value of CreateThread() was compared against INVALID_HANDLE_VALUE against null, causing the error handling code to run at the wrong time.
There are a lot of other uses of INVALID_HANDLE_VALUE I found that looked questionable, but which I left alone. Most of these were used to initialize HANDLE-typed variables and as a sentinel to see if those variables remained unset to a "real" value.
Fixes#427
* set identifying environment variable for new connections
Set a new 'WT_SESSION' environment variable when creating new terminal
connections to allow shells to detect a unique Windows Terminal session.
The value of the variable is a stringified GUID as returned by
CoCreateGuid.
How verified:
- "razzle" & vs debug build
- runut
- manual inspection
* * use winrt::guid type for connection guid
* use Utils::GuidToString for guid stringification
* expose guid parameter in ITerminalConnection idl
* - poke guid through ITerminalConnection
- misc. review fixes
- throw if CreateConPty fails in ConhostConnection::Start
- apply [[nodiscard]] and noexcept in various places
* - simplify environment variable extraction in UpdateEnvironmentMapW
* - use Utils::CreateGuid instead of CoCreateGuid in ConHostConnection()
