fix terminal output close bugs

[brianignacio5]

Fix task output parsing for extension tasks on Windows.
Fix emit close event code !== 0

Fix #287
Fix #290

[Elijahg]

This seems to be broken for me. Whilst the "building" notification does now disappear upon failure, the terminal now behaves more similarly to the non-VSCode one in that the build status no longer has a newline for each completed file, and just overwrites the existing line. This is fine, but it doesn't work properly in VSCode as it just keeps overwriting part of the existing line rather than clearing the whole line:

Screen.Recording.2021-01-18.at.20.22.48.mp4

Presumably as a result of this, the build failure messages are also pushed onto that single line, so it's impossible to see the error causing the build to fail, and the "problems" view in VSCode shows nothing. In a non-VSCode terminal the errors are written properly onto separate lines.