only get all workspace tasks if default glob configured

[meganrogge]

another regression from #141230

fixes https://github.com/microsoft/vscode/issues/185960

this dramatically speeds up the execution of the build task and now only the necessary extension gets activated.

tested the single repo and multi repo cases

while it's true that this will break for people that are using it, it's probably a small minority and they'll make an issue and i can say you can enable it with this setting.

[meganrogge]

I wonder if instead of a setting, we can figure this out when the tasks.json is parsed?

EDIT: no, because still requires activating the extension that contributes it

[meganrogge]

instead of the setting, @tyriar suggested I try _getConfiguration