Make isc_result a static enum

Remove the dynamic registration of result codes.  Convert isc_result_t
from unsigned + #defines into 32-bit enum type in grand unified
<isc/result.h> header.  Keep the existing values of the result codes
even at the expense of the description and identifier tables being
unnecessary large.

Additionally, add couple of:

    switch (result) {
    [...]
    default:
        break;
    }

statements where compiler now complains about missing enum values in the
switch statement.

bin/tools/mdig.c

@@ -29,6 +29,7 @@
 #include <isc/parseint.h>
 #include <isc/print.h>
 #include <isc/random.h>
+#include <isc/result.h>
 #include <isc/sockaddr.h>
 #include <isc/string.h>
 #include <isc/task.h>
@@ -46,12 +47,9 @@
 #include <dns/rdatatype.h>
 #include <dns/request.h>
 #include <dns/resolver.h>
-#include <dns/result.h>
 #include <dns/types.h>
 #include <dns/view.h>
 
-#include <dst/result.h>
-
 #include <bind9/getaddresses.h>
 
 #define CHECK(str, x)                                                       \
@@ -2075,8 +2073,6 @@ main(int argc, char *argv[]) {
 
 	RUNCHECK(isc_app_start());
 
-	dns_result_register();
-
 	if (isc_net_probeipv4() == ISC_R_SUCCESS) {
 		have_ipv4 = true;
 	}