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/bacint.c

@@ -23,7 +23,7 @@ int encode_unsigned16(uint8_t *apdu, uint16_t value)
     return 2;
 }
 
-int decode_unsigned16(uint8_t *apdu, uint16_t *value)
+int decode_unsigned16(const uint8_t *apdu, uint16_t *value)
 {
     if (apdu && value) {
         *value  = (uint16_t)apdu[0] << 8;
@@ -44,7 +44,7 @@ int encode_unsigned24(uint8_t *apdu, uint32_t value)
     return 3;
 }
 
-int decode_unsigned24(uint8_t *apdu, uint32_t *value)
+int decode_unsigned24(const uint8_t *apdu, uint32_t *value)
 {
     if (apdu && value) {
         *value  = (uint32_t)apdu[0] << 16;
@@ -67,7 +67,7 @@ int encode_unsigned32(uint8_t *apdu, uint32_t value)
     return 4;
 }
 
-int decode_unsigned32(uint8_t *apdu, uint32_t *value)
+int decode_unsigned32(const uint8_t *apdu, uint32_t *value)
 {
     if (apdu && value) {
         *value  = (uint32_t)apdu[0] << 24;
@@ -105,7 +105,7 @@ int encode_unsigned40(uint8_t *buffer, uint64_t value)
  * @param       value - pointer to 64-bit value to store the decoded value
  * @return      Returns the number of bytes decoded
  */
-int decode_unsigned40(uint8_t *buffer, uint64_t *value)
+int decode_unsigned40(const uint8_t *buffer, uint64_t *value)
 {
     if (buffer && value) {
         *value  = (uint64_t)buffer[0] << 32;
@@ -144,7 +144,7 @@ int encode_unsigned48(uint8_t *buffer, uint64_t value)
  * @param       value - pointer to 64-bit value to store the decoded value
  * @return      Returns the number of bytes decoded
  */
-int decode_unsigned48(uint8_t *buffer, uint64_t *value)
+int decode_unsigned48(const uint8_t *buffer, uint64_t *value)
 {
     if (buffer && value) {
         *value  = (uint64_t)buffer[0] << 40;
@@ -185,7 +185,7 @@ int encode_unsigned56(uint8_t *buffer, uint64_t value)
  * @param       value - pointer to 64-bit value to store the decoded value
  * @return      Returns the number of bytes decoded
  */
-int decode_unsigned56(uint8_t *buffer, uint64_t *value)
+int decode_unsigned56(const uint8_t *buffer, uint64_t *value)
 {
     if (buffer && value) {
         *value  = (uint64_t)buffer[0] << 48;
@@ -228,7 +228,7 @@ int encode_unsigned64(uint8_t *buffer, uint64_t value)
  * @param       value - pointer to 64-bit value to store the decoded value
  * @return      Returns the number of bytes decoded
  */
-int decode_unsigned64(uint8_t *buffer, uint64_t *value)
+int decode_unsigned64(const uint8_t *buffer, uint64_t *value)
 {
     if (buffer && value) {
         *value  = (uint64_t)buffer[0] << 56;
@@ -294,7 +294,7 @@ int encode_signed8(uint8_t *apdu, int8_t value)
     return 1;
 }
 
-int decode_signed8(uint8_t *apdu, int32_t *value)
+int decode_signed8(const uint8_t *apdu, int32_t *value)
 {
     if (apdu && value) {
         /* negative - bit 7 is set */
@@ -319,7 +319,7 @@ int encode_signed16(uint8_t *apdu, int16_t value)
     return 2;
 }
 
-int decode_signed16(uint8_t *apdu, int32_t *value)
+int decode_signed16(const uint8_t *apdu, int32_t *value)
 {
     if (apdu && value) {
         /* negative - bit 7 is set */
@@ -346,7 +346,7 @@ int encode_signed24(uint8_t *apdu, int32_t value)
     return 3;
 }
 
-int decode_signed24(uint8_t *apdu, int32_t *value)
+int decode_signed24(const uint8_t *apdu, int32_t *value)
 {
     if (apdu && value) {
         /* negative - bit 7 is set */
@@ -375,7 +375,7 @@ int encode_signed32(uint8_t *apdu, int32_t value)
     return 4;
 }
 
-int decode_signed32(uint8_t *apdu, int32_t *value)
+int decode_signed32(const uint8_t *apdu, int32_t *value)
 {
     if (apdu && value) {
         *value  = (int32_t)apdu[0] << 24;