Updating synthetic package_config.json generation directory (#4387)

This was causing files in `web/` and other non-package roots from following versions in the generated `package_config.json`. 

Fixes #4302

Author: Markzipan

build_modules/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 5.1.8
+
+- Generate synthetic `package_config.json` in the root of its synthetic test directory. Fixes sources in `web/` and related directories not obeying version constraints.
+
 ## 5.1.7
 
 - Add entrypoint file deserialization logic to FrontendServerState.

build_modules/lib/src/scratch_space.dart

@@ -117,8 +117,8 @@ String _scratchSpacePackageConfig(String rootConfig, Uri packageConfigUri) {
     if (rootUri == _currentDirUri) {
       assert(!foundRoot);
       foundRoot = true;
-      package['packageUri'] = '';
-      package['rootUri'] = '../packages/${package['name']}/';
+      package['rootUri'] = '../';
+      package['packageUri'] = 'packages/${package['name']}/';
     } else {
       package['rootUri'] = '../packages/${package['name']}/';
       package.remove('packageUri');

build_modules/pubspec.yaml

@@ -1,5 +1,5 @@
 name: build_modules
-version: 5.1.7
+version: 5.1.8
 description: >-
   Builders to analyze and split Dart code into individually compilable modules
   based on imports.