Rework the MAP metric. (#8931)

- The new implementation is more strict as only binary labels are accepted. The previous implementation converts values greater than 1 to 1.
- Deterministic GPU. (no atomic add).
- Fix top-k handling.
- Precise definition of MAP. (There are other variants on how to handle top-k).
- Refactor GPU ranking tests.

tests/cpp/common/test_ranking_utils.cu

@@ -95,4 +95,10 @@ TEST(NDCGCache, InitFromGPU) {
   ctx.UpdateAllowUnknown(Args{{"gpu_id", "0"}});
   TestNDCGCache(&ctx);
 }
+
+TEST(MAPCache, InitFromGPU) {
+  Context ctx;
+  ctx.UpdateAllowUnknown(Args{{"gpu_id", "0"}});
+  TestMAPCache(&ctx);
+}
 }  // namespace xgboost::ltr