Convert benchmark registration to be programmatic & add other RE backends

This makes it easier to add more benchmark cases, while ensuring they
run across all of RenderEngine's backends (GaneshGL, GaneshVk,
GraphiteVk), or across other parameters.

Also remove the obsolete flag guard that was disabling
BM_homescreen_edgeExtension

Bug: b/425760461
Test: atest librenderengine_bench
Flag: EXEMPT b/c test only, but GraphiteVk is guarded by compile flags
Change-Id: I576e017999910a95f332930bd934df42f24da7cf