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/special_event.c

@@ -29,7 +29,7 @@
  * @return length of the APDU buffer, or BACNET_STATUS_ERROR if unable to decode
  */
 int bacnet_special_event_decode(
-    uint8_t *apdu, int apdu_size, BACNET_SPECIAL_EVENT *value)
+    const uint8_t *apdu, int apdu_size, BACNET_SPECIAL_EVENT *value)
 {
     int len = 0;
     int apdu_len = 0;
@@ -97,7 +97,8 @@ int bacnet_special_event_decode(
  * @param value - BACnetSpecialEvent structure
  * @return length of the APDU buffer, or 0 if not able to encode
  */
-int bacnet_special_event_encode(uint8_t *apdu, BACNET_SPECIAL_EVENT *value)
+int bacnet_special_event_encode(
+    uint8_t *apdu, const BACNET_SPECIAL_EVENT *value)
 {
     int apdu_len = 0;
     int len;
@@ -153,7 +154,7 @@ int bacnet_special_event_encode(uint8_t *apdu, BACNET_SPECIAL_EVENT *value)
  * @return length of the APDU buffer, or 0 if not able to encode
  */
 int bacnet_special_event_context_encode(
-    uint8_t *apdu, uint8_t tag_number, BACNET_SPECIAL_EVENT *value)
+    uint8_t *apdu, uint8_t tag_number, const BACNET_SPECIAL_EVENT *value)
 {
     int len = 0;
     int apdu_len = 0;
@@ -184,7 +185,7 @@ int bacnet_special_event_context_encode(
  * @param value - BACnetSpecialEvent structure
  * @return length of the APDU buffer, or BACNET_STATUS_ERROR if unable to decode
  */
-int bacnet_special_event_context_decode(uint8_t *apdu,
+int bacnet_special_event_context_decode(const uint8_t *apdu,
     int apdu_size,
     uint8_t tag_number,
     BACNET_SPECIAL_EVENT *value)
@@ -222,10 +223,10 @@ int bacnet_special_event_context_decode(uint8_t *apdu,
  * @return true if the same
  */
 bool bacnet_special_event_same(
-    BACNET_SPECIAL_EVENT *value1, BACNET_SPECIAL_EVENT *value2)
+    const BACNET_SPECIAL_EVENT *value1, const BACNET_SPECIAL_EVENT *value2)
 {
     BACNET_APPLICATION_DATA_VALUE adv1, adv2;
-    BACNET_TIME_VALUE *tv1, *tv2;
+    const BACNET_TIME_VALUE *tv1, *tv2;
     int ti;
 
     if (value1->periodTag != value2->periodTag ||