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>

ports/linux/mstpsnap.c

@@ -84,7 +84,7 @@ uint16_t MSTP_Get_Send(
  */
 void MSTP_Send_Frame(
     struct mstp_port_struct_t *mstp_port,
-    uint8_t * buffer,
+    const uint8_t * buffer,
     uint16_t nbytes)
 {
     (void)mstp_port;
@@ -141,7 +141,7 @@ static int network_init(const char *name, int protocol)
 }
 
 static void snap_received_packet(
-    struct mstp_port_struct_t *mstp_port, int sockfd)
+    const struct mstp_port_struct_t *mstp_port, int sockfd)
 {
     uint16_t mtu_len = 0; /* number of octets of packet saved in file */
     unsigned i = 0; /* counter */