Make install:openapi create the folders it needs #606

Summary

install:openapi fails when the module has no resources folder or the project has no public/assets/OpenApiUi folder. Part of the PHP 8.1 update (#595), found while smoke-testing the API templates (#597).

Why

• A module generated with module:generate -t DefaultApi has no resources folder. install:openapi then fails with mkdir(): No such file or directory, because it creates resources/openapi with LocalFileSystemAdapter::makeDirectory(), which calls mkdir() without the recursive flag. The DemoApi template ships a resources folder, so it works.
• When public/assets/OpenApiUi does not exist, copyResources() fails with copy(public/assets/OpenApiUi\index.css): Failed to open stream, because it copies into the folder without creating it.

Proposed change

• Create modules/<Name>/resources/openapi including its missing parents.
• Create public/assets/OpenApiUi before copying the Swagger UI files into it.
• Extend OpenApiCommandTest with one case for each missing folder.

Out of scope

• Making makeDirectory() recursive for every caller.

Breaking changes

• None.

Acceptance criteria

• php qt install:openapi <module> succeeds for a module generated from the DefaultApi template
• php qt install:openapi <module> succeeds when public/assets/OpenApiUi does not exist
• composer test, composer cs:check, composer phpstan and composer rector:check pass