Make most of functions const correct (#714)

* Make most of the functions const correct

Used clang-tidy and sonarlint to help find places where const could
pretty easily applied. Also lot of hand work.

This commit does not yet touch handlers and typedefs of those.

* Fix Arduino uno handler_who_is() has extra parenthesis

For some reason there is extra parenthesis. Remove it this is more
likely buildable.

* Bugfix/bacapp: Fix uninitilized array_index

We have changed bacapp_snprintf_value() to be const correct. After that
we got

```
/home/runner/work/bacnet-stack/bacnet-stack/src/bacnet/bacapp.c:3183:27: warning: 4th function call argument is an uninitialized value [core.CallAndMessage]
                ret_val = bacapp_snprintf_weeklyschedule(
                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 warning generated.
```

So analyzer could now spot that we do not actually initilize array_index
at all. Fix this by setting array_index to zero. Note that I actually do
not know if zeroing is right thing to do here. I choose zero as if this
has worked before it is most likely that it will work with zero value.

* cmake: Add and ignore Wwrite-strings compiler option

Wwrite-strings helps find places where const correctness is broken.

Example it will warn about these

```C

void func1(char* str);

func("test") /* "test" is const so we should not pass it to func1().

char* func2()
{
  return "test"; /* func2() should return const char*.
}
```

We still need to ignore it as not all are fixed but let's add it already
so we remember that it should be opened at some point.

---------

Co-authored-by: Kari Argillander <kari.argillander@fidelix.com>

src/bacnet/datalink/mstp.c

@@ -98,7 +98,7 @@ static __inline__ void printf_master(const char *format, ...)
             x++;                     \
     }
 
-bool MSTP_Line_Active(struct mstp_port_struct_t *mstp_port)
+bool MSTP_Line_Active(const struct mstp_port_struct_t *mstp_port)
 {
     if (!mstp_port) {
         return false;
@@ -162,7 +162,7 @@ uint16_t MSTP_Create_Frame(uint8_t *buffer,
     uint8_t frame_type,
     uint8_t destination,
     uint8_t source,
-    uint8_t *data,
+    const uint8_t *data,
     uint16_t data_len)
 {
     uint8_t crc8 = 0xFF; /* used to calculate the crc value */
@@ -259,7 +259,7 @@ void MSTP_Create_And_Send_Frame(struct mstp_port_struct_t *mstp_port,
     uint8_t frame_type,
     uint8_t destination,
     uint8_t source,
-    uint8_t *data,
+    const uint8_t *data,
     uint16_t data_len)
 {
     uint16_t len = 0; /* number of bytes to send */
@@ -268,7 +268,7 @@ void MSTP_Create_And_Send_Frame(struct mstp_port_struct_t *mstp_port,
         MSTP_Create_Frame(mstp_port->OutputBuffer, mstp_port->OutputBufferSize,
             frame_type, destination, source, data, data_len);
 
-    MSTP_Send_Frame(mstp_port, (uint8_t *)&mstp_port->OutputBuffer[0], len);
+    MSTP_Send_Frame(mstp_port, &mstp_port->OutputBuffer[0], len);
     /* FIXME: be sure to reset SilenceTimer() after each octet is sent! */
 }
 
@@ -778,7 +778,7 @@ bool MSTP_Master_Node_FSM(struct mstp_port_struct_t *mstp_port)
                 uint8_t frame_type = mstp_port->OutputBuffer[2];
                 uint8_t destination = mstp_port->OutputBuffer[3];
                 MSTP_Send_Frame(mstp_port,
-                    (uint8_t *)&mstp_port->OutputBuffer[0], (uint16_t)length);
+                    &mstp_port->OutputBuffer[0], (uint16_t)length);
                 mstp_port->FrameCount++;
                 switch (frame_type) {
                     case FRAME_TYPE_BACNET_DATA_EXPECTING_REPLY:
@@ -1159,7 +1159,7 @@ bool MSTP_Master_Node_FSM(struct mstp_port_struct_t *mstp_port)
                  * frame  */
                 /* and enter the IDLE state to wait for the next frame. */
                 MSTP_Send_Frame(mstp_port,
-                    (uint8_t *)&mstp_port->OutputBuffer[0], (uint16_t)length);
+                    &mstp_port->OutputBuffer[0], (uint16_t)length);
                 mstp_port->master_state = MSTP_MASTER_STATE_IDLE;
                 /* clear our flag we were holding for comparison */
                 mstp_port->ReceivedValidFrame = false;
@@ -1255,8 +1255,7 @@ void MSTP_Slave_Node_FSM(struct mstp_port_struct_t *mstp_port)
             /* and enter the IDLE state to wait for the next frame.
                 */
             MSTP_Send_Frame(mstp_port,
-                (uint8_t *)&mstp_port->OutputBuffer[0],
-                (uint16_t)length);
+                &mstp_port->OutputBuffer[0], (uint16_t)length);
             /* clear our flag we were holding for comparison */
             mstp_port->ReceivedValidFrame = false;
         } else if (mstp_port->SilenceTimer((void *)mstp_port) >