Add dispose to WindowsShellHelper

Fixes #31951

Rely on it cleaning up after itself after taskkill.exe kills the
process tree. Telling node-pty to clean up was causing a native
exception as the shell process no longer exists.

One concern is that this could leak process handles but I verified
that the OS cleans this up https://msdn.microsoft.com/en-us/library/windows/desktop/ms686722(v=vs.85).aspx

Fixes #31782

Update PHP grammar (temporarily from a fork that contains the previous version + an important change to fix #30448)

Fixes #31876

Fixes #21215

Update dotnet build task

Fixes #31822