Add Warning Quality Check Build Task 🔨

[kllysng]

With the new task, I've configured the build to:

• fail if the number of warnings has increased since the previous build - no new warnings!
• show warning statistics to show the changes in number of warnings grouped by task/code file/object

I have not selected this option:

• Force fewer warnings
• Allow Variance - we don't want the number of warnings to creep up.

Build Quality Checks Warnings Policy documentation: https://github.com/MicrosoftPremier/VstsExtensions/blob/master/BuildQualityChecks/en-US/WarningsPolicy.md#evaluateTaskWarnings

[jmprieur]

LGTM
Thanks @kellyyangsong

[jennyf19]

nice