revert: "fix(@ngtools/webpack): improve fallbacking for path mapping"

This reverts commit 47f937e.

This commit had a few issues detected by the NativeScript project. It is
likely that they would have affected more users (and libraries) and so
it is safer to revert now and investigate later. Will likely be fixed in
6.2 by refactoring this whole plugin properly.

Author: hansl

packages/ngtools/webpack/src/paths-plugin.ts

@@ -154,21 +154,14 @@ export function resolveWithPaths(
 
   // If TypeScript gives us a `.d.ts`, it is probably a node module
   if (moduleFilePath.endsWith('.d.ts')) {
-    const pathNoExtension = moduleFilePath.slice(0, -5);
-    const pathDirName = path.dirname(moduleFilePath);
-    const packageRootPath = path.join(pathDirName, 'package.json');
-    const jsFilePath = `${pathNoExtension}.js`;
-
-    if (host.fileExists(pathNoExtension)) {
-        // This is mainly for secondary entry points
-        // ex: 'node_modules/@angular/core/testing.d.ts' -> 'node_modules/@angular/core/testing'
-        request.request = pathNoExtension;
-    } else if (host.fileExists(packageRootPath)) {
-        // Let webpack resolve the correct module format
-        request.request = pathDirName;
-    } else if (host.fileExists(jsFilePath)) {
-        // Otherwise, if there is a file with a .js extension use that
+    // If in a package, let webpack resolve the package
+    const packageRootPath = path.join(path.dirname(moduleFilePath), 'package.json');
+    if (!host.fileExists(packageRootPath)) {
+      // Otherwise, if there is a file with a .js extension use that
+      const jsFilePath = moduleFilePath.slice(0, -5) + '.js';
+      if (host.fileExists(jsFilePath)) {
         request.request = jsFilePath;
+      }
     }
 
     callback(null, request);