[SYCL] Add tests for zero-length USM memset/memcpy preserving the dependency chain (#500)

The corresponding fix in SYCL: intel/llvm#4727

Author: dnmokhov

SYCL/USM/dep_events.cpp

@@ -31,7 +31,10 @@ int main() {
   event eMemset1 = q.memset(x, 0, sizeof(int), event{});              // x = 0
   event eMemset2 = q.memset(y, 0, sizeof(int), std::vector<event>{}); // y = 0
   event eFill = q.fill(x, 1, 1, {eMemset1, eMemset2});                // x = 1
-  event eMemcpy = q.memcpy(y, x, sizeof(int), eFill);                 // y = 1
+  event eNoOpMemset = q.memset(x, 0, 0, eFill);       // 0 count, so x remains 1
+  event eNoOpMemcpy = q.memcpy(x, y, 0, eNoOpMemset); // 0 count, so x remains 1
+  event eNoOpCopy = q.copy(y, x, 0, eNoOpMemcpy);     // 0 count, so x remains 1
+  event eMemcpy = q.memcpy(y, x, sizeof(int), eNoOpCopy);             // y = 1
   event eCopy = q.copy(y, z, 1, eMemcpy);                             // z = 1
   event ePrefetch = q.prefetch(z, sizeof(int), eCopy);                //
   q.single_task<class kernel>(ePrefetch, [=] { *z *= 2; }).wait();    // z = 2