sf: Add basic implementation of onVsyncIdle

To adopt the new AIDL composer callback API, the patch changes the
architecture to pass HWC2::ComposerCallback directly in the
registerCallback function. The underlying implementations can use their
own bridge to adapt with different versions of callback APIs.

Bug: 194068871
Test: atest libsurfaceflinger_unittest
Change-Id: I08bcf481747f38805fb2527e18293585ede51554
diff --git a/services/surfaceflinger/DisplayHardware/HWC2.h b/services/surfaceflinger/DisplayHardware/HWC2.h
index 57eb128..0a605a8 100644
--- a/services/surfaceflinger/DisplayHardware/HWC2.h
+++ b/services/surfaceflinger/DisplayHardware/HWC2.h
@@ -72,6 +72,7 @@
     virtual void onComposerHalVsyncPeriodTimingChanged(hal::HWDisplayId,
                                                        const hal::VsyncPeriodChangeTimeline&) = 0;
     virtual void onComposerHalSeamlessPossible(hal::HWDisplayId) = 0;
+    virtual void onComposerHalVsyncIdle(hal::HWDisplayId) = 0;
 
 protected:
     ~ComposerCallback() = default;