surfaceflinger: Generate unique layer names

Add a counter to layer names to make it clear when there are duplicates.

    layer foo#0
    layer foo#1
    layer bar#0
    layer bar#1
    layer bar#2

Bug: b/32543755
Test: Build, install, run game with duplicate layers, see unique names.

Change-Id: I915531d7adbdc506c429b86a685665fb6c56d25e