Add system_random and random_bytes for js target

core/crypto/rand_generic.odin

@@ -1,7 +1,7 @@
 package crypto
 
-when ODIN_OS != .Linux && ODIN_OS != .OpenBSD && ODIN_OS != .Windows {
-	_rand_bytes :: proc (dst: []byte) {
+when ODIN_OS != .Linux && ODIN_OS != .OpenBSD && ODIN_OS != .Windows && ODIN_OS != .JS {
+	_rand_bytes :: proc(dst: []byte) {
 		unimplemented("crypto: rand_bytes not supported on this OS")
 	}
 }

core/crypto/rand_js.odin

@@ -0,0 +1,20 @@
+package crypto
+
+foreign import "odin_env"
+foreign odin_env {
+	@(link_name = "rand_bytes")
+	env_rand_bytes :: proc "contextless" (buf: []byte) ---
+}
+
+_MAX_PER_CALL_BYTES :: 65536
+
+_rand_bytes :: proc(dst: []byte) {
+	dst := dst
+
+	for len(dst) > 0 {
+		to_read := min(len(dst), _MAX_PER_CALL_BYTES)
+		env_rand_bytes(dst[:to_read])
+
+		dst = dst[to_read:]
+	}
+}

core/math/rand/system_js.odin

@@ -0,0 +1,11 @@
+package rand
+
+foreign import "odin_env"
+foreign odin_env {
+	rand :: proc "contextless" () -> f64 ---
+}
+
+@(require_results)
+_system_random :: proc() -> u64 {
+	return u64(rand() * 0x1fffffffffffff)
+}