Support for `#:ref` / `#:project` references in Source Generators

When using FBA in C#, we can reference other projects with
`#:ref` or `#:project` directives.

However, when developing Source Generator Analyzers, it is unclear how to
consume or recognize these references. I would like to know:

How can a Source Generator access metadata/symbols from projects referenced via `#:ref` or `#:project`?
Is there existing support for this scenario, or is it planned for future SDK updates?
Currently, I could not find documentation or samples that explain this integration.
If this is not supported yet, I would like to request feature support so that
Source Generators can properly work with FBA project references.

Start by investigating how FBA `#:ref` and `#:project` directives are processed and how Source Generator Analyzers receive referenced project metadata or symbols. No files, tests, or entry points are named; determine whether support already exists, then identify the SDK behavior or documentation needed to make the integration clear.

Written by the indexing model from the issue text.