Improve Windows support in integrated terminal October 2017

[Tyriar]

This is a plan item for terminal work in the October iteration, in rough order of priority:

• Terminal leaks processes Terminal leaks processes #26807
• Trashcan button kills entire terminal process tree including non-console apps Trashcan button kills entire terminal process tree including non-console apps #35492
• Wrapped lines lead to wrong problems Wrapped lines lead to wrong problems #32042
• Scrolling via mousewheel in the terminal scrolls by a lot on Windows (about 12 lines) Scrolling via mousewheel in the terminal scrolls by a lot on Windows (~12 lines) #35111
• Terminals launched with invalid paths hang during creation and never emit onExit Terminals launched with invalid paths hang during creation and never emit onExit #31301
• Terminal doesn't handle PowerShell's space escape character correctly Terminal doesn't handle PowerShell's space escape character correctly #33584

[Tyriar]

/cc @dbaeumer

[equinusocio]

@Tyriar what about this one?
#35963

[Tyriar]

@equinusocio that one's not Windows. I suspect that process may be detaching itself or something as there haven't been any reports of it happening on macOS or Linux.

[dbaeumer]

@Tyriar could we add #33584 to the list. I have requests to better handle spaces in commands and for bash I propose to use \ as a space escape character. Would be cool if I could propose the backtick for PowerShell. This has the advantage of not dealing with quotes which always complicates things.

[Tyriar]

@dbaeumer sure I'll see if I can get to it for October. Could you provide repro steps in that issue where you expect it to work, either as a task.json or terminal.integrated.shellArgs.windows?

[ghiscoding]

@Tyriar what about this one?
#30638
I find it a bit annoying that a cls doesn't clear the history entirely as it comes back in some situations and it seems to be Windows only.

[dbaeumer]

@Tyriar regarding #33584: I retested this and it seems to work using this task now in a workspace that has a test folder directory. The task is:

		{
			"type": "shell",
			"taskName": "dir",
			"command": "dir test` folder"
		}

Terminal must be PowerShell. The internal launch args are:

[eamodio]

@Tyriar maybe #36989 can be included here too?