Cannot resolve symbol 'void'... until Unity Editor is opened

### Description of problem:
From a clean boot, when I open Rider without opening Unity, and I open a unity project in Rider, Rider is unable to resolve any symbols, even built-in language keywords like "void". As soon as the project is opened in the Unity Editor, the problem vanishes.

### Expected behaviour:
Rider should be able to resolve symbols and allow the user to work on the code regardless of whether or not the Unity Editor is also running.

### Reproduction Steps

1. Have a pre-existing Unity project available on your drive that uses C# and has csproj's generated
2. Reboot the computer
3. Open JetBrains Rider. Open the Unity Project's solution.
4. Open any code file. See errors throughout.

### Known Workaround

Opening the Unity Editor to the same project resolves the issues, but this is not always ideal.

### System Specs
Fedora 40
JetBrains Rider 2024.1.5#RD-241.18968.19
Rider Unity Support Plugin bundled 241.18968.19
Unity 2022.3.7f1

No source files, tests, or entry points are named. Reproduce the issue using the listed Fedora, Rider, and Unity versions by opening the generated solution before opening Unity; done means built-in symbols and project symbols resolve without launching the Unity Editor.

Written by the indexing model from the issue text.