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/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 8ca9982..bf5f138 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -631,6 +631,7 @@
     void onComposerHalVsyncPeriodTimingChanged(hal::HWDisplayId,
                                                const hal::VsyncPeriodChangeTimeline&) override;
     void onComposerHalSeamlessPossible(hal::HWDisplayId) override;
+    void onComposerHalVsyncIdle(hal::HWDisplayId) override;
 
     // ICompositor overrides: