Root file detection in multiple entry project

[pfoerster]

Discussed in #916

^{Originally posted by OopsYao August 7, 2023}
The support of multiple files is great, but it seems like that the detection algorithm is vague in terms of projects with multiple entries. E.g., we have two main files (like our article and beamer) sharing a common dependency (like a tikz diagram), in this case, how do I control which (or both) root file(s) to build / forward search when editing the dependency file?

In my opinion, a prompt (that can remember user's choice via project-scoped cache) or a project config file is fine. 👀

% main1.tex
\documentclass{article}

\begin{document}
Article.
\input{dep}
\end{document}

% main2.tex
\documentclass{beamer}

\begin{document}
Beamer.
\input{dep}
\end{document}

% dep.tex
A common dependency like a diagram.
```</div>