Add handling for classes deriving from Capability in capturing type logic

Author: noti0na1

compiler/src/dotty/tools/dotc/cc/Setup.scala

@@ -728,6 +728,9 @@ class Setup extends PreRecheck, SymTransformer, SetupAPI:
                 else if cls.isPureClass then
                   // is cls is known to be pure, nothing needs to be added to self type
                   selfInfo
+                else if cls.derivesFrom(defn.Caps_Capability) then
+                  CapturingType(cinfo.selfType, CaptureSet.csImpliedByCapability)
+                  // CapturingType(cinfo.selfType, CaptureSet.universal)
                 else if !cls.isEffectivelySealed && !cls.baseClassHasExplicitNonUniversalSelfType then
                   // assume {cap} for completely unconstrained self types of publicly extensible classes
                   CapturingType(cinfo.selfType, CaptureSet.universal)