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>

ports/pic18f97j60/mstp.c

@@ -118,17 +118,17 @@
             x++;                     \
     }
 
-bool MSTP_Line_Active(volatile struct mstp_port_struct_t *mstp_port)
+bool MSTP_Line_Active(const volatile struct mstp_port_struct_t *mstp_port)
 {
     return (mstp_port->EventCount > Nmin_octets);
 }
 
 unsigned MSTP_Create_Frame(uint8_t *buffer, /* where frame is loaded */
     unsigned buffer_len, /* amount of space available */
-    uint8_t frame_type, /* type of frame to send - see defines */
+    uint8_t frame_type,  /* type of frame to send - see defines */
     uint8_t destination, /* destination address */
-    uint8_t source, /* source address */
-    uint8_t *data, /* any data to be sent - may be null */
+    uint8_t source,      /* source address */
+    const uint8_t *data, /* any data to be sent - may be null */
     unsigned data_len)
 { /* number of bytes of data (up to 501) */
     uint8_t crc8 = 0xFF; /* used to calculate the crc value */
@@ -181,7 +181,7 @@ void MSTP_Create_And_Send_Frame(
     uint8_t frame_type, /* type of frame to send - see defines */
     uint8_t destination, /* destination address */
     uint8_t source, /* source address */
-    uint8_t *data, /* any data to be sent - may be null */
+    const uint8_t *data, /* any data to be sent - may be null */
     unsigned data_len)
 { /* number of bytes of data (up to 501) */
     uint8_t buffer[DLMSTP_MPDU_MAX] = { 0 }; /* buffer for sending */

ports/pic18f97j60/mstp.h

@@ -142,15 +142,15 @@ extern "C" {
 
     /* returns true if line is active */
     bool MSTP_Line_Active(
-        volatile struct mstp_port_struct_t *mstp_port);
+        const volatile struct mstp_port_struct_t *mstp_port);
 
     unsigned MSTP_Create_Frame(
         uint8_t * buffer,       /* where frame is loaded */
         unsigned buffer_len,    /* amount of space available */
         uint8_t frame_type,     /* type of frame to send - see defines */
         uint8_t destination,    /* destination address */
-        uint8_t source, /* source address */
-        uint8_t * data, /* any data to be sent - may be null */
+        uint8_t source,         /* source address */
+        const uint8_t * data,   /* any data to be sent - may be null */
         unsigned data_len);     /* number of bytes of data (up to 501) */
 
 

ports/pic18f97j60/rs485.c

@@ -42,7 +42,7 @@ volatile uint8_t RS485_Tx_Buffer[NEXT_POWER_OF_2(DLMSTP_MPDU_MAX)];
  *****************************************************************************/
 void RS485_Send_Frame(
     volatile struct mstp_port_struct_t *mstp_port, /* port specific data */
-    uint8_t *buffer, /* frame to send (up to 501 bytes of data) */
+    const uint8_t *buffer, /* frame to send (up to 501 bytes of data) */
     uint16_t nbytes)
 { /* number of bytes of data (up to 501) */
     uint16_t i = 0; /* loop counter */

ports/pic18f97j60/rs485.h

@@ -28,8 +28,8 @@ extern "C" {
 
     void RS485_Send_Frame(
         volatile struct mstp_port_struct_t *mstp_port,  /* port specific data */
-        uint8_t * buffer,       /* frame to send (up to 501 bytes of data) */
-        uint16_t nbytes);       /* number of bytes of data (up to 501) */
+        const uint8_t * buffer,     /* frame to send (up to 501 bytes of data) */
+        uint16_t nbytes);           /* number of bytes of data (up to 501) */
 
     /* returns true if there is more data waiting */
     bool RS485_Check_UART_Data(