webassembly: Implement MICROPY_PY_RANDOM_SEED_INIT_FUNC.

Signed-off-by: Damien George <damien@micropython.org>

ports/webassembly/library.h

@@ -29,3 +29,4 @@
 extern void mp_js_write(const char *str, mp_uint_t len);
 extern int mp_js_ticks_ms(void);
 extern void mp_js_hook(void);
+extern uint32_t mp_js_random_u32(void);

ports/webassembly/library.js

@@ -63,4 +63,11 @@ mergeInto(LibraryManager.library, {
             }
         }
     },
+
+    // Node prior to v19 did not expose "crypto" as a global, so make sure it exists.
+    mp_js_random_u32__postset:
+        "if (globalThis.crypto === undefined) { globalThis.crypto = require('crypto'); }",
+
+    mp_js_random_u32: () =>
+        globalThis.crypto.getRandomValues(new Uint32Array(1))[0],
 });

ports/webassembly/mpconfigport.h

@@ -49,6 +49,8 @@
 #define MICROPY_FLOAT_IMPL          (MICROPY_FLOAT_IMPL_DOUBLE)
 #define MICROPY_USE_INTERNAL_ERRNO  (1)
 #define MICROPY_USE_INTERNAL_PRINTF (0)
+
+#define MICROPY_PY_RANDOM_SEED_INIT_FUNC (mp_js_random_u32())
 #ifndef MICROPY_VFS
 #define MICROPY_VFS                 (1)
 #endif
@@ -95,3 +97,5 @@ typedef long mp_off_t;
 // _GNU_SOURCE must be defined to get definitions of DT_xxx symbols from dirent.h.
 #define _GNU_SOURCE
 #endif
+
+uint32_t mp_js_random_u32(void);