ArPow should default to error on prebuilt baseline comparison

[mmitche]

• This issue is blocking
• This issue is causing unreasonable pain

Today, a warning is emitted (due to ContinueOnError) when the comparison task fails. This is fine as most repos treat warnings as errors. But this has caused issues in roslyn where this is not the case.

Release Note Category

• Feature changes/additions
• Bug fixes
• Internal Infrastructure Improvements

Release Note Description