Align verbose warnings (-Wconf / @nowarn) with Scala 3

[lrytz]

Once scala/scala3#12857 is merged:

• In -Wconf, remove the info-verbose / iv action, rename the warning-verbose / wv action to verbose / v
• Support @nowarn("verbose") in source code. Update the @nowarn annotation's Scaladocs.
• Improve the "verbose" warnings output to explicitly display the filters that match the warning (cat=deprecation, site=a.b.C, ...)

[dwijnand]

• In -Wconf, remove the info-verbose / iv action, rename the warning-verbose / wv action to verbose / v

Deprecate?

[SethTisue]

@lrytz is this a blocker for 2.13.7?

[lrytz]

Nah, I don't think so