Avoid memsets for constant collections where possible

• Analysis to determine which collection constants actually need to be memset to zero.
• NoResetConstant schedule to encode analysis result persistently.
• Use NoResetConstant in backends to not generate memsets.

juno_samples/implicit_clone/src/gpu.sch

@@ -15,6 +15,8 @@ dce(*);
 infer-schedules(*);
 
 gcm(*);
-float-collections(*);
-dce(*);
-gcm(*);
+fixpoint {
+  float-collections(*);
+  dce(*);
+  gcm(*);
+}