Cellular: Replace UARTSerial references with BufferedSerial

`BufferedSerial` is `UARTSerial` renamed to convey the original purpose
of the class. It is the recommended buffered I/O serial class.

Author: hugueskamba

UNITTESTS/features/cellular/framework/AT/at_cellularcontext/at_cellularcontexttest.cpp

@@ -531,7 +531,7 @@ TEST_F(TestAT_CellularContext, set_file_handle)
     AT_CellularContext ctx(at, &dev);
     ctx.set_file_handle(&fh1);
 
-    UARTSerial ss(NC, NC);
+    BufferedSerial ss(NC, NC);
 
     ctx.set_file_handle(&ss, PTC0, true);
     ctx.enable_hup(true);

UNITTESTS/features/cellular/framework/AT/at_cellularcontext/unittest.cmake

@@ -37,7 +37,7 @@ set(unittest-test-sources
   stubs/randLIB_stub.cpp
   stubs/Semaphore_stub.cpp
   stubs/us_ticker_stub.cpp
-  stubs/UARTSerial_stub.cpp
+  stubs/BufferedSerial_stub.cpp
   stubs/SerialBase_stub.cpp
   stubs/CellularContext_stub.cpp
   stubs/CellularUtil_stub.cpp

UNITTESTS/features/cellular/framework/AT/at_cellulardevice/unittest.cmake

@@ -38,7 +38,7 @@ set(unittest-test-sources
   stubs/NetworkStack_stub.cpp
   stubs/AT_CellularContext_stub.cpp
   stubs/Semaphore_stub.cpp
-  stubs/UARTSerial_stub.cpp
+  stubs/BufferedSerial_stub.cpp
   stubs/SerialBase_stub.cpp
   stubs/CellularStateMachine_stub.cpp
   stubs/CellularContext_stub.cpp

UNITTESTS/features/cellular/framework/device/athandler/unittest.cmake

@@ -24,7 +24,7 @@ set(unittest-test-sources
   stubs/EventQueue_stub.cpp
   stubs/FileHandle_stub.cpp
   stubs/us_ticker_stub.cpp
-  stubs/UARTSerial_stub.cpp
+  stubs/BufferedSerial_stub.cpp
   stubs/SerialBase_stub.cpp
   stubs/mbed_assert_stub.cpp
   stubs/mbed_poll_stub.cpp

UNITTESTS/features/cellular/framework/device/cellularcontext/cellularcontexttest.cpp

@@ -165,7 +165,7 @@ class testContext : public CellularContext
 
 	}
 #if (DEVICE_SERIAL && DEVICE_INTERRUPTIN) || defined(DOXYGEN_ONLY)
-    virtual void set_file_handle(UARTSerial *serial, PinName dcd_pin = NC, bool active_high = false)
+    virtual void set_file_handle(BufferedSerial *serial, PinName dcd_pin = NC, bool active_high = false)
     {
 
     }

UNITTESTS/features/cellular/framework/device/cellularcontext/unittest.cmake

@@ -29,7 +29,7 @@ set(unittest-test-sources
   stubs/CellularStateMachine_stub.cpp
   stubs/EventQueue_stub.cpp
   stubs/mbed_assert_stub.cpp
-  stubs/UARTSerial_stub.cpp
+  stubs/BufferedSerial_stub.cpp
   stubs/SerialBase_stub.cpp
   stubs/ATHandler_stub.cpp
   stubs/AT_CellularNetwork_stub.cpp

UNITTESTS/features/cellular/framework/device/cellulardevice/unittest.cmake

@@ -23,7 +23,7 @@ set(unittest-test-sources
   stubs/CellularStateMachine_stub.cpp
   stubs/EventQueue_stub.cpp
   stubs/mbed_assert_stub.cpp
-  stubs/UARTSerial_stub.cpp
+  stubs/BufferedSerial_stub.cpp
   stubs/SerialBase_stub.cpp
   stubs/ATHandler_stub.cpp
   stubs/AT_CellularNetwork_stub.cpp

UNITTESTS/features/cellular/framework/device/cellularstatemachine/unittest.cmake

@@ -23,7 +23,7 @@ set(unittest-test-sources
   stubs/CellularDevice_stub.cpp
   stubs/EventQueue_stub.cpp
   stubs/mbed_assert_stub.cpp
-  stubs/UARTSerial_stub.cpp
+  stubs/BufferedSerial_stub.cpp
   stubs/SerialBase_stub.cpp
   stubs/ATHandler_stub.cpp
   stubs/AT_CellularNetwork_stub.cpp

UNITTESTS/stubs/AT_CellularContext_stub.cpp

@@ -51,7 +51,7 @@ AT_CellularContext::~AT_CellularContext()
 {
 }
 
-void AT_CellularContext::set_file_handle(UARTSerial *serial, PinName dcd_pin, bool active_high)
+void AT_CellularContext::set_file_handle(BufferedSerial *serial, PinName dcd_pin, bool active_high)
 {
 }
 

UNITTESTS/stubs/AT_CellularDevice_stub.cpp

@@ -65,7 +65,7 @@ nsapi_error_t AT_CellularDevice::release_at_handler(ATHandler *at_handler)
     }
 }
 
-CellularContext *AT_CellularDevice::create_context(UARTSerial *serial, const char *const apn, PinName dcd_pin,
+CellularContext *AT_CellularDevice::create_context(BufferedSerial *serial, const char *const apn, PinName dcd_pin,
                                                    bool active_high, bool cp_req, bool nonip_req)
 {
 }