Remove additional sf transaction when constructing a leash

The leash needs to be visible on creation otherwise when reparenting
the leash, the leashed layer may be hidden for a moment. This is because
Transaction#show can be deferred but Transaction#reparent cannot.

This change adds a layer flag to allow creating effect layers without
a color fill so we can avoid an additional sf transaction.

Fixes: 157646690
Test: go/wm-smoke
Test: atest SurfaceFlinger_test
Change-Id: I3d8a4f4820d7b8fb05daab697c25cff8def612c1