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/bacreal.c

@@ -21,7 +21,7 @@
 
 /* from clause 20.2.6 Encoding of a Real Number Value */
 /* returns the number of apdu bytes consumed */
-int decode_real(uint8_t *apdu, float *real_value)
+int decode_real(const uint8_t *apdu, float *real_value)
 {
     union {
         uint8_t byte[4];
@@ -49,7 +49,7 @@ int decode_real(uint8_t *apdu, float *real_value)
     return 4;
 }
 
-int decode_real_safe(uint8_t *apdu, uint32_t len_value, float *real_value)
+int decode_real_safe(const uint8_t *apdu, uint32_t len_value, float *real_value)
 {
     if (len_value != 4) {
         if (real_value) {
@@ -93,7 +93,7 @@ int encode_bacnet_real(float value, uint8_t *apdu)
 
 /* from clause 20.2.7 Encoding of a Double Precision Real Number Value */
 /* returns the number of apdu bytes consumed */
-int decode_double(uint8_t *apdu, double *double_value)
+int decode_double(const uint8_t *apdu, double *double_value)
 {
     union {
         uint8_t byte[8];
@@ -129,7 +129,8 @@ int decode_double(uint8_t *apdu, double *double_value)
     return 8;
 }
 
-int decode_double_safe(uint8_t *apdu, uint32_t len_value, double *double_value)
+int decode_double_safe(
+    const uint8_t *apdu, uint32_t len_value, double *double_value)
 {
     if (len_value != 8) {
         if (double_value) {