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.

lib/dns/dst_api.c

@@ -47,6 +47,8 @@
 
 #define DST_KEY_INTERNAL
 
+#include <isc/result.h>
+
 #include <dns/fixedname.h>
 #include <dns/keyvalues.h>
 #include <dns/name.h>
@@ -55,8 +57,6 @@
 #include <dns/ttl.h>
 #include <dns/types.h>
 
-#include <dst/result.h>
-
 #include "dst_internal.h"
 
 #define DST_AS_STR(t) ((t).value.as_textregion.base)
@@ -190,8 +190,6 @@ dst_lib_init(isc_mem_t *mctx, const char *engine) {
 
 	UNUSED(engine);
 
-	dst_result_register();
-
 	memset(dst_t_func, 0, sizeof(dst_t_func));
 	RETERR(dst__hmacmd5_init(&dst_t_func[DST_ALG_HMACMD5]));
 	RETERR(dst__hmacsha1_init(&dst_t_func[DST_ALG_HMACSHA1]));