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.h

@@ -25,7 +25,7 @@ extern "C" {
         uint16_t value);
     BACNET_STACK_EXPORT
     int decode_unsigned16(
-        uint8_t * apdu,
+        const uint8_t * apdu,
         uint16_t * value);
     BACNET_STACK_EXPORT
     int encode_unsigned24(
@@ -33,7 +33,7 @@ extern "C" {
         uint32_t value);
     BACNET_STACK_EXPORT
     int decode_unsigned24(
-        uint8_t * apdu,
+        const uint8_t * apdu,
         uint32_t * value);
     BACNET_STACK_EXPORT
     int encode_unsigned32(
@@ -41,7 +41,7 @@ extern "C" {
         uint32_t value);
     BACNET_STACK_EXPORT
     int decode_unsigned32(
-        uint8_t * apdu,
+        const uint8_t * apdu,
         uint32_t * value);
 #ifdef UINT64_MAX
     BACNET_STACK_EXPORT
@@ -50,7 +50,7 @@ extern "C" {
         uint64_t value);
     BACNET_STACK_EXPORT
     int decode_unsigned40(
-        uint8_t * buffer,
+        const uint8_t * buffer,
         uint64_t * value);
     BACNET_STACK_EXPORT
     int encode_unsigned48(
@@ -58,7 +58,7 @@ extern "C" {
         uint64_t value);
     BACNET_STACK_EXPORT
     int decode_unsigned48(
-        uint8_t * buffer,
+        const uint8_t * buffer,
         uint64_t * value);
     BACNET_STACK_EXPORT
     int encode_unsigned56(
@@ -66,7 +66,7 @@ extern "C" {
         uint64_t value);
     BACNET_STACK_EXPORT
     int decode_unsigned56(
-        uint8_t * buffer,
+        const uint8_t * buffer,
         uint64_t * value);
     BACNET_STACK_EXPORT
     int encode_unsigned64(
@@ -74,7 +74,7 @@ extern "C" {
         uint64_t value);
     BACNET_STACK_EXPORT
     int decode_unsigned64(
-        uint8_t * buffer,
+        const uint8_t * buffer,
         uint64_t * value);
 #endif
 
@@ -92,7 +92,7 @@ extern "C" {
         int8_t value);
     BACNET_STACK_EXPORT
     int decode_signed8(
-        uint8_t * apdu,
+        const uint8_t * apdu,
         int32_t * value);
     BACNET_STACK_EXPORT
     int encode_signed16(
@@ -100,7 +100,7 @@ extern "C" {
         int16_t value);
     BACNET_STACK_EXPORT
     int decode_signed16(
-        uint8_t * apdu,
+        const uint8_t * apdu,
         int32_t * value);
     BACNET_STACK_EXPORT
     int encode_signed24(
@@ -108,7 +108,7 @@ extern "C" {
         int32_t value);
     BACNET_STACK_EXPORT
     int decode_signed24(
-        uint8_t * apdu,
+        const uint8_t * apdu,
         int32_t * value);
     BACNET_STACK_EXPORT
     int encode_signed32(
@@ -116,7 +116,7 @@ extern "C" {
         int32_t value);
     BACNET_STACK_EXPORT
     int decode_signed32(
-        uint8_t * apdu,
+        const uint8_t * apdu,
         int32_t * value);
 
 #ifdef __cplusplus