[routing-manager] use Heap::Array for OnMeshPrefixArray (#9592)

This commit updates `RoutingManager` to use heap allocated array
for `OnMeshPrefixArray` under `BORDER_ROUTING_USE_HEAP_ENABLE`
config.

This commit also updates the `toranj-config-posix` header to
explicitly disable `BORDER_ROUTING_USE_HEAP_ENABLE` under the POSIX
config to validate builds with this config disabled. This aligns with
the main purpose of the `toranj` posix build config, which is to
validate builds under different configs (run from the
`toranj-unittest` job in the `toranj.yml` GitHub action workflow).

src/core/border_router/routing_manager.cpp

@@ -362,7 +362,11 @@ void RoutingManager::Stop(void)
 
     SendRouterAdvertisement(kInvalidateAllPrevPrefixes);
 
+#if OPENTHREAD_CONFIG_BORDER_ROUTING_USE_HEAP_ENABLE
+    mAdvertisedPrefixes.Free();
+#else
     mAdvertisedPrefixes.Clear();
+#endif
 
     mDiscoveredPrefixTable.RemoveAllEntries();
     mDiscoveredPrefixStaleTimer.Stop();

src/core/border_router/routing_manager.hpp

@@ -54,6 +54,7 @@
 #include "common/array.hpp"
 #include "common/error.hpp"
 #include "common/heap_allocatable.hpp"
+#include "common/heap_array.hpp"
 #include "common/linked_list.hpp"
 #include "common/locator.hpp"
 #include "common/message.hpp"
@@ -954,7 +955,12 @@ private:
 
     typedef Ip6::Prefix OnMeshPrefix;
 
-    class OnMeshPrefixArray : public Array<OnMeshPrefix, kMaxOnMeshPrefixes>
+    class OnMeshPrefixArray :
+#if OPENTHREAD_CONFIG_BORDER_ROUTING_USE_HEAP_ENABLE
+        public Heap::Array<OnMeshPrefix>
+#else
+        public Array<OnMeshPrefix, kMaxOnMeshPrefixes>
+#endif
     {
     public:
         void Add(const OnMeshPrefix &aPrefix);

tests/toranj/openthread-core-toranj-config-posix.h

@@ -47,4 +47,7 @@
 
 #define OPENTHREAD_POSIX_CONFIG_SPINEL_HDLC_INTERFACE_ENABLE 1
 
+// Disabled explicitly on posix `toranj` to validate the build with this config
+#define OPENTHREAD_CONFIG_BORDER_ROUTING_USE_HEAP_ENABLE 0
+
 #endif /* OPENTHREAD_CORE_TORANJ_CONFIG_POSIX_H_ */

tests/toranj/openthread-core-toranj-config-simulation.h

@@ -59,6 +59,8 @@
 
 #define OPENTHREAD_CONFIG_HEAP_EXTERNAL_ENABLE 1
 
+#define OPENTHREAD_CONFIG_BORDER_ROUTING_USE_HEAP_ENABLE 1
+
 #define OPENTHREAD_CONFIG_RADIO_STATS_ENABLE 0
 
 #endif /* OPENTHREAD_CORE_TORANJ_CONFIG_SIMULATION_H_ */