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/npdu.h

@@ -71,7 +71,7 @@ extern "C" {
         uint8_t * npdu,
         BACNET_ADDRESS * dest,
         BACNET_ADDRESS * src,
-        BACNET_NPDU_DATA * npdu_data);
+        const BACNET_NPDU_DATA * npdu_data);
 
     BACNET_STACK_EXPORT
     int bacnet_npdu_encode_pdu(
@@ -79,7 +79,7 @@ extern "C" {
         uint16_t pdu_size,
         BACNET_ADDRESS * dest,
         BACNET_ADDRESS * src,
-        BACNET_NPDU_DATA * npdu_data);
+        const BACNET_NPDU_DATA * npdu_data);
 
     BACNET_STACK_EXPORT
     void npdu_encode_npdu_data(
@@ -97,19 +97,19 @@ extern "C" {
     BACNET_STACK_EXPORT
     void npdu_copy_data(
         BACNET_NPDU_DATA * dest,
-        BACNET_NPDU_DATA * src);
+        const BACNET_NPDU_DATA * src);
 
     BACNET_STACK_DEPRECATED("Use bacnet_npdu_decode() instead")
     BACNET_STACK_EXPORT
     int npdu_decode(
-        uint8_t * npdu,
+        const uint8_t * npdu,
         BACNET_ADDRESS * dest,
         BACNET_ADDRESS * src,
         BACNET_NPDU_DATA * npdu_data);
 
     BACNET_STACK_EXPORT
     int bacnet_npdu_decode(
-        uint8_t * npdu,
+        const uint8_t * npdu,
         uint16_t pdu_len,
         BACNET_ADDRESS * dest,
         BACNET_ADDRESS * src,
@@ -117,7 +117,7 @@ extern "C" {
 
     BACNET_STACK_EXPORT
     bool npdu_confirmed_service(
-        uint8_t *pdu,
+        const uint8_t *pdu,
         uint16_t pdu_len);
 
 #ifdef __cplusplus