Make users aware of (new) validation results

[f1ames]

As in title. Related to #6.

Currently there is no real visual cue when a validation has been performed - which makes it confusing... users have to figure out to open the SARIF viewer themselves - and if there are new validation errors due to a central policy update there won't be any CTA to handle/inspect those.

Not sure what we can do? Open the SARIF panel? (May require some changes in SARIF extension or a workaround because SARIF ext public API is quite minimalistic.) Show a popup notification? Doesn't VS-Code have some infrastructure for this? I'm seeing alerts/popups in the bottom right all the time..

Reported by @olensmar.

[f1ames]

My take on this would be that we want to notify users of new errors/warnings? So if validation runs and the number of errors remains the same maybe we shouldn't bother the user (assuming the he/she saw validation panel already - which should be true as it gets open on initial validation run).

So if subsequent validation runs yields different results, either we could reopen validation panel or show notification saying that there are new errors/warnings (with a button to open validation panel).

[olensmar]

thanks @f1ames - a notification with an action to open the panel seems sufficient to me!?