Provide progress indicator for language/debug server startup

[daviwil]

Some users are attempting to start debugging just after loading a PowerShell script for the first time in a session. In some cases the language and debug servers have not yet finished initializing so there needs to be some indication in the UI that the extension isn't fully initialized yet.

[daviwil]

Adding this to 0.8.0 but I might fix it in a patch release if it turns out to be a common source of confusion.

[daviwil]

Also need to have a better error message when the user tries to run the debugger when PSES hasn't finished starting.

[rkeithhill]

BTW, depending on what's in the user's profile this can take several seconds. I've seen PowerShell take as much as ~15 seconds to cold start (on one of my slower machines). The 5.1 version of PowerShell will tell you how long it took to process your profile - giving you a strong hint that if you want PowerShell to load faster - lighten up your profile. I wonder if we could do the same? Display a progress message like "Processing your PowerShell profile scripts...", "Importing and initializing the PowerShellEditorServices module...".

[daviwil]

Based on the way I do startup I'm not sure if I'll be able to give updates to the UI between those phases. I launch powershell.exe and it basically takes care of loading the PSES module. Maybe after loading is complete I could give some message if a certain part of the process takes longer than a certain time expectation?

[daviwil]

I've decided to do this work for 0.8.0 since there are a few things I want to do to make it easier for users to easily understand the state of PSES when the extension is running:

• Implement new status bar item like the C# extension which makes it obvious whether PSES is initializing, running, or failed.
• Create a new output channel which will contain client-side PSES log output
• Hook up a command to the status bar item which shows the PSES log output window in case any error occurs

[daviwil]

I've pushed a branch with the initial work on this here: https://github.com/PowerShell/vscode-powershell/tree/daviwil/extension-status. Will continue after I've completed some other things.