[tcat][ble] improve internal state management of ble simulation platform (#12913)

This adds sIsEnabled for more realistic BLE simulation platform behavior. Also
improves internal disconnection state management, per review comments.

Adds asynchronous calling of otPlatBleGapOnDisconnected() to avoid doing the
'disconnected' callback twice, per review comments. A unit test is extended to
verify that the callback happens once.

For test_platform.cpp 2 instances of '#ifdef' are fixed to '#if'.

tests/unit/test_platform.cpp

@@ -35,7 +35,7 @@
 #include <sys/time.h>
 #include <openthread/platform/flash.h>
 
-#ifdef OPENTHREAD_CONFIG_BLE_TCAT_ENABLE
+#if OPENTHREAD_CONFIG_BLE_TCAT_ENABLE
 #include <openthread/tcat.h>
 #include <openthread/platform/ble.h>
 #endif
@@ -800,7 +800,7 @@ OT_TOOL_WEAK otPlatMcuPowerState otPlatGetMcuPowerState(otInstance *aInstance) {
 
 OT_TOOL_WEAK otError otPlatSetMcuPowerState(otInstance *aInstance, otPlatMcuPowerState aState) { return OT_ERROR_NONE; }
 #endif // OPENTHREAD_CONFIG_NCP_ENABLE_MCU_POWER_STATE_CONTROL
-#ifdef OPENTHREAD_CONFIG_BLE_TCAT_ENABLE
+#if OPENTHREAD_CONFIG_BLE_TCAT_ENABLE
 
 uint8_t  sPlatBleLastAdvSetData[OT_TCAT_ADVERTISEMENT_MAX_LEN];
 uint16_t sPlatBleLastAdvSetDataLen = 0;
@@ -842,7 +842,9 @@ otError otPlatBleGapAdvStop(otInstance *aInstance)
 
 otError otPlatBleGapDisconnect(otInstance *aInstance)
 {
-    OT_UNUSED_VARIABLE(aInstance);
+    // Honor the platform contract: report completion of the disconnection via the callback.
+    // Normally this call is done asynchronously, but for unit testing purposes we make the reentrant call.
+    otPlatBleGapOnDisconnected(aInstance, 0);
     return OT_ERROR_NONE;
 }