lib: fix --preserve-symlinks-main

Fixed resolving relative imports when symlink to main file called without file extension

Fixies: nodejs#41000

lib/internal/modules/cjs/loader.js

@@ -469,8 +469,8 @@ function tryPackage(requestPath, exts, isMain, originalPath) {
 }
 
 /**
- * Check if the file exists and is not a directory if using `--preserve-symlinks` and `isMain` is false, keep symlinks
- * intact, otherwise resolve to the absolute realpath.
+ * Check if the file exists and is not a directory if using `--preserve-symlinks` and `isMain` is false or
+ * `--preserve-symlinks-main` and `isMain` is true , keep symlinks intact, otherwise resolve to the absolute realpath.
  * @param {string} requestPath The path to the file to load.
  * @param {boolean} isMain Whether the file is the main module.
  */
@@ -480,6 +480,9 @@ function tryFile(requestPath, isMain) {
   if (getOptionValue('--preserve-symlinks') && !isMain) {
     return path.resolve(requestPath);
   }
+  if (getOptionValue('--preserve-symlinks-main') && isMain) {
+    return path.resolve(requestPath);
+  }
   return toRealPath(requestPath);
 }