Is your feature request related to a problem? Please describe.
If I call checkSyntax very frequently I'm going be writing a ton of temp files. Would be nice to avoid that overhead and just feed in the string through stdin.

Describe the solution you'd like
checkSyntax using stdin

Describe alternatives you've considered
overhead might not be a big deal?

Additional context
Related to re-architecture work in Almenon/AREPL-vscode#439. I'd like to throw away pythonGuiLibraryIsPresent and just check syntax all the time. Less code needed and much less hacky because one doesn't have to list out each GUI library.