File upload exercises: Fix an issue with old file submissions not being deleted

[theblobinthesky]

Checklist

General

• I tested all changes and their related features with all corresponding user types on a test server.
• This is a small issue that I tested locally and was confirmed by another developer on a test server.
• Language: I followed the guidelines for inclusive, diversity-sensitive, and appreciative language.
• I chose a title conforming to the naming conventions for pull requests.

Server

• Important: I implemented the changes with a very good performance and prevented too many (unnecessary) database calls.
• I followed the coding and design guidelines.
• I added multiple integration tests (Spring) related to the features (with a high test coverage).
• I added pre-authorization annotations according to the guidelines and checked the course groups for all new REST Calls (security).
• I documented the Java code using JavaDoc style.

Client

• Important: I implemented the changes with a very good performance, prevented too many (unnecessary) REST calls and made sure the UI is responsive, even with large data.
• I followed the coding and design guidelines.
• Following the theming guidelines, I specified colors only in the theming variable files and checked that the changes look consistent in both the light and the dark theme.
• I added multiple integration tests (Jest) related to the features (with a high test coverage), while following the test guidelines.
• I added authorities to all new routes and checked the course groups for displaying navigation elements (links, buttons).
• I documented the TypeScript code using JSDoc style.
• I added multiple screenshots/screencasts of my UI changes.
• I translated all newly inserted strings into English and German.

Changes affecting Programming Exercises

• I tested all changes and their related features with all corresponding user types on Test Server 1 (Atlassian Suite).
• I tested all changes and their related features with all corresponding user types on Test Server 2 (Jenkins and Gitlab).

Motivation and Context

This fixes the issue #7275.

Description

The FileUploadSubmission class contains the filePath attribute which is a public path and has to be converted to an actual path on the file system before being used. In this case the onDelete() function did not convert the path and therefore no old submission file from a file upload exercise could ever be deleted.
I think this is where the breaking change happened: aca8f44#diff-afbf7c4cfa2c701ea17f5d3fc9cae4f94e88f182921364471f35e9f3355e0302R37
Since i wanted to avoid using the FilePathService inside of an entity, i reverted back to the implementation before it broke.
I also added an error message to FileService's schedulePathForDeletion when the file to-be-deleted does not exist to catch such errors reliably in the future.

Steps for Testing

Prerequisites:

• 1 Student
• 1 Programming Exercise with Complaints enabled

1. Upload a file to the file upload exercise.
2. Upload another file to replace the old submission.
3. Acknowledge the old submission file has been deleted and only the new one is left.

Review Progress

Performance Review

• I (as a reviewer) confirm that the client changes (in particular related to REST calls and UI responsiveness) are implemented with a very good performance
• I (as a reviewer) confirm that the server changes (in particular related to database calls) are implemented with a very good performance

Code Review

• Code Review 1
• Code Review 2

Manual Tests

• Test 1
• Test 2

Exam Mode Test

• Test 1
• Test 2

Test Coverage

Screenshots

[JohannesStoehr]

Code looks good to me

[Strohgelaender]

code lgtm