Add support for coverage markup

[tampajohn]

Adding coverage highlighting to vscode-go. Adds setting "go.coverageOnSave" and command for performing coverage for current package. Addresses some of the desires of #80.

[tecbot]

@tampajohn Awesome 👍

One thing what I found: If the cursor is on a tested line and I want to add a new line with new code, then the next line and all new following lines will have the same background color as the tested line (green or red). Would be better to reset the background color for the new line/code if possible.

[tampajohn]

@tecbot Hmmmm, I'm not super sure where the best place to tie into this is... @lukehoban I know I could do something using registerOnTypeFormattingEditProvider, but that seems kinda invasive... do you know a good place to handle resetting coverage when a document is dirty?

[lukehoban]

Depends a bit on what experience you want exactly.

You could try workspace.onDidChangeTextDocument which sends a notification when any open text document changes.

But do you think it makes sense to instead try to keep the coverage information around even after you make edits?

[tecbot]

+1 remove the coverage if start editing the code

[tampajohn]

@tecbot Removing coverage for the file that's been edited, thanks for the onDidChangeTextDocument pointer @lukehoban

[rs]

What is the status of this PR? What’s missing for its merging?

[lukehoban]

Finally got a chance to re-review this, and looks good.

I've merged this in now along with a few minor changes.

Thanks @tampajohn, and apologies for the 4 month delay 😄.