core/crypto: Add a HAS_RAND_BYTES constant

core/crypto/rand_js.odin

@@ -6,8 +6,12 @@ foreign odin_env {
 	env_rand_bytes :: proc "contextless" (buf: []byte) ---
 }
 
+HAS_RAND_BYTES :: true
+
+@(private)
 _MAX_PER_CALL_BYTES :: 65536 // 64kiB
 
+@(private)
 _rand_bytes :: proc(dst: []byte) {
 	dst := dst
 
@@ -18,7 +22,3 @@ _rand_bytes :: proc(dst: []byte) {
 		dst = dst[to_read:]
 	}
 }
-
-_has_rand_bytes :: proc() -> bool {
-	return true
-}