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/basic/sys/filename.c

@@ -9,9 +9,9 @@
 #include <string.h>
 #include "bacnet/basic/sys/filename.h"
 
-char *filename_remove_path(const char *filename_in)
+const char *filename_remove_path(const char *filename_in)
 {
-    char *filename_out = (char *)filename_in;
+    const char *filename_out = filename_in;
 
     /* allow the device ID to be set */
     if (filename_in) {
@@ -24,7 +24,7 @@ char *filename_remove_path(const char *filename_in)
             filename_out++;
         } else {
             /* no slash in filename */
-            filename_out = (char *)filename_in;
+            filename_out = filename_in;
         }
     }