Avoid hardcoded stat bits in nodejs code. NFC (#21904)

I noticed this while reviewing #21902.

Author: sbc100

src/generated_struct_info32.json

@@ -383,7 +383,10 @@
         "S_IFMT": 61440,
         "S_IFREG": 32768,
         "S_IFSOCK": 49152,
+        "S_IRGRP": 32,
+        "S_IROTH": 4,
         "S_IRUGO": 292,
+        "S_IRUSR": 256,
         "S_IRWXO": 7,
         "S_IRWXUGO": 511,
         "S_ISVTX": 512,

src/generated_struct_info64.json

@@ -383,7 +383,10 @@
         "S_IFMT": 61440,
         "S_IFREG": 32768,
         "S_IFSOCK": 49152,
+        "S_IRGRP": 32,
+        "S_IROTH": 4,
         "S_IRUGO": 292,
+        "S_IRUSR": 256,
         "S_IRWXO": 7,
         "S_IRWXUGO": 511,
         "S_ISVTX": 512,

src/library_nodefs.js

@@ -71,7 +71,7 @@ addToLibrary({
         if (NODEFS.isWindows) {
           // Node.js on Windows never represents permission bit 'x', so
           // propagate read bits to execute bits
-          stat.mode = stat.mode | ((stat.mode & 292) >> 2);
+          stat.mode |= (stat.mode & {{{ cDefs.S_IRUSR | cDefs.S_IRGRP | cDefs.S_IROTH }}}) >> 2;
         }
       } catch (e) {
         if (!e.code) throw e;

src/library_wasmfs_node.js

@@ -21,7 +21,7 @@ addToLibrary({
     if (wasmfsNodeIsWindows) {
       // Node.js on Windows never represents permission bit 'x', so
       // propagate read bits to execute bits
-      stat.mode = stat.mode | ((stat.mode & 292) >> 2);
+      stat.mode |= (stat.mode & {{{ cDefs.S_IRUSR | cDefs.S_IRGRP | cDefs.S_IROTH }}}) >> 2;
     }
     return stat;
   },

src/struct_info.json

@@ -30,7 +30,10 @@
             "S_IFSOCK",
             "S_IFBLK",
             "S_IFLNK",
-            "S_IFCHR"
+            "S_IFCHR",
+            "S_IRUSR",
+            "S_IRGRP",
+            "S_IROTH"
         ],
         "structs": {
             "stat": [