[nexus] migrate publish meshcop service cert test to nexus (openthread#13186)

This commit migrates the legacy Thread certification test
'test_publish_meshcop_service.py' to the C++ simulation test suite
in the Nexus platform.

To avoid redundancy and keep the test suite clean, the coverage
is consolidated directly within 'tests/nexus/test_border_agent.cpp'
instead of introducing a new redundant test file.

Consolidated coverage and changes:
- Extended the state bitmap parser and 'ValidateMeshCoPTxtData' in
  'test_border_agent.cpp' to verify Backbone Router (BBR) active
  and primary flags (kFlagBbrIsActive, kFlagBbrIsPrimary) when
  OPENTHREAD_CONFIG_BACKBONE_ROUTER_ENABLE is enabled.
- Added a new test block in 'TestBorderAgentServiceRegistration' to
  enable Backbone Router on node0, verify that BBR active and primary
  flags are dynamically advertised in the MeshCoP TXT record over
  mDNS, and verify that disabling BBR correctly updates the TXT
  record state bitmap.
- Fully deleted the legacy Python certification script
  'test_publish_meshcop_service.py' from 'thread-cert'.

Author: jwhui

tests/nexus/test_border_agent.cpp

@@ -1311,6 +1311,10 @@ void ValidateMeshCoPTxtData(TxtData &aTxtData, Node &aNode, bool aExpectVendorIn
     static constexpr uint32_t kThreadRoleLeader             = 3 << 9;
     static constexpr uint32_t kFlagEpskcSupported           = 1 << 11;
     static constexpr uint32_t kFlagAdmitterSupported        = 1 << 14;
+#if OPENTHREAD_CONFIG_BACKBONE_ROUTER_ENABLE
+    static constexpr uint32_t kFlagBbrIsActive  = 1 << 7;
+    static constexpr uint32_t kFlagBbrIsPrimary = 1 << 8;
+#endif
 
     MeshCoP::BorderAgent::Id id;
     BaTxtData::Info          info;
@@ -1449,6 +1453,35 @@ void ValidateMeshCoPTxtData(TxtData &aTxtData, Node &aNode, bool aExpectVendorIn
         VerifyOrQuit(!info.mStateBitmap.mAdmitterSupported);
     }
 
+#if OPENTHREAD_CONFIG_BACKBONE_ROUTER_ENABLE
+    {
+        bool bbrEnabled = aNode.Get<Mle::Mle>().IsAttached() && aNode.Get<BackboneRouter::Local>().IsEnabled();
+        bool bbrPrimary = aNode.Get<Mle::Mle>().IsAttached() && aNode.Get<BackboneRouter::Local>().IsPrimary();
+
+        if (bbrEnabled)
+        {
+            VerifyOrQuit(stateBitmap & kFlagBbrIsActive);
+            VerifyOrQuit(info.mStateBitmap.mBbrIsActive);
+        }
+        else
+        {
+            VerifyOrQuit(!(stateBitmap & kFlagBbrIsActive));
+            VerifyOrQuit(!info.mStateBitmap.mBbrIsActive);
+        }
+
+        if (bbrPrimary)
+        {
+            VerifyOrQuit(stateBitmap & kFlagBbrIsPrimary);
+            VerifyOrQuit(info.mStateBitmap.mBbrIsPrimary);
+        }
+        else
+        {
+            VerifyOrQuit(!(stateBitmap & kFlagBbrIsPrimary));
+            VerifyOrQuit(!info.mStateBitmap.mBbrIsPrimary);
+        }
+    }
+#endif
+
     if (aExpectVendorInfo)
     {
         const char *expectedVendorName = (aVendorName != nullptr) ? aVendorName : aNode.Get<VendorInfo>().GetName();
@@ -2356,6 +2389,55 @@ void TestBorderAgentServiceRegistration(void)
     VerifyOrQuit(foundService);
 
     node0.Get<Dns::Multicast::Core>().FreeIterator(*iterator);
+
+    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+    Log("Enable Backbone Router on node0 and validate state bitmap updates");
+
+    node0.Get<BorderRouter::InfraIf>().Init(kInfraIfIndex, true);
+    node0.Get<BorderRouter::RoutingManager>().Init();
+    SuccessOrQuit(node0.Get<BorderRouter::RoutingManager>().SetEnabled(true));
+    node0.Get<BackboneRouter::Local>().SetEnabled(true);
+
+    nexus.AdvanceTime(10 * Time::kOneSecondInMsec);
+
+    iterator = node0.Get<Dns::Multicast::Core>().AllocateIterator();
+    VerifyOrQuit(iterator != nullptr);
+
+    foundService = false;
+    while (node0.Get<Dns::Multicast::Core>().GetNextService(*iterator, service, entryState) == kErrorNone)
+    {
+        if (StringMatch(service.mServiceType, "_meshcop._udp"))
+        {
+            VerifyOrQuit(!foundService);
+            foundService = true;
+            ValidateRegisteredServiceData(service, node0);
+        }
+    }
+    VerifyOrQuit(foundService);
+    node0.Get<Dns::Multicast::Core>().FreeIterator(*iterator);
+
+    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+    Log("Disable Backbone Router on node0 and validate state bitmap updates");
+
+    node0.Get<BackboneRouter::Local>().SetEnabled(false);
+
+    nexus.AdvanceTime(10 * Time::kOneSecondInMsec);
+
+    iterator = node0.Get<Dns::Multicast::Core>().AllocateIterator();
+    VerifyOrQuit(iterator != nullptr);
+
+    foundService = false;
+    while (node0.Get<Dns::Multicast::Core>().GetNextService(*iterator, service, entryState) == kErrorNone)
+    {
+        if (StringMatch(service.mServiceType, "_meshcop._udp"))
+        {
+            VerifyOrQuit(!foundService);
+            foundService = true;
+            ValidateRegisteredServiceData(service, node0);
+        }
+    }
+    VerifyOrQuit(foundService);
+    node0.Get<Dns::Multicast::Core>().FreeIterator(*iterator);
 }
 
 void TestBorderAgentServiceRegistrationRename(void)