fix(@schematics/angular): configure library sourceRoot to project root

[alan-agius4]

Sets sourceRoot for generated libraries to the project root instead of ${projectRoot}/src.

This ensures that test discovery can properly discover test files across secondary entry points without needing parent directory traversal.

Fixes #33467

[gemini-code-assist]

Code Review

This pull request changes the sourceRoot of generated libraries from ${projectRoot}/src to projectRoot. However, this introduces a directory structure inconsistency where subsequent schematic elements (like components) are generated under ${projectRoot}/lib/ instead of ${projectRoot}/src/lib/. To resolve this, it is recommended to update buildDefaultPath to correctly handle libraries where sourceRoot is equal to projectRoot.

[gemini-code-assist]

Setting sourceRoot to projectRoot introduces a directory structure inconsistency when generating subsequent schematic elements (like components, services, etc.) within the library.

The Issue

1. The library's initial files and entry point are generated under ${projectRoot}/src/lib/.
2. However, buildDefaultPath (in packages/schematics/angular/utility/workspace.ts) resolves the default path using project.sourceRoot:

   const root = project.sourceRoot ? `/${project.sourceRoot}/` : `/${project.root}/src/`;

   Since sourceRoot is now projectRoot, buildDefaultPath will resolve to ${projectRoot}/lib/ instead of ${projectRoot}/src/lib/.
3. This causes subsequent components to be generated in ${projectRoot}/lib/ (as seen in the updated test assertion in index_spec.ts line 331), which is inconsistent with the initial library structure and will not be resolved/compiled correctly by default.

Suggested Fix

To support setting sourceRoot to projectRoot for test discovery while maintaining consistent generation paths, buildDefaultPath in packages/schematics/angular/utility/workspace.ts should be updated to handle libraries where sourceRoot is equal to root:

export function buildDefaultPath(project: workspaces.ProjectDefinition): string {
  const projectType = project.extensions['projectType'];
  let root = project.sourceRoot ? `/${project.sourceRoot}/` : `/${project.root}/src/`;
  if (projectType === ProjectType.Library && project.sourceRoot === project.root) {
    root = `/${project.root}/src/`;
  }
  const projectDirName = projectType === ProjectType.Application ? 'app' : 'lib';

  return `${root}${projectDirName}`;
}