--library cannot stage a project's installed dependencies and does not follow dependency changes #1889

Staging a project's dependencies with --library is manual and does not stay current:

• Every dependency has to be named by hand; there is no way to say "the dependencies this project uses". For Java (dependencies ship as jars) and C# (NuGet packages ship assemblies) there was no way to stage them from what is installed at all.
• A dependency named as a source directory is parsed again on every rebuild the refresher starts after an edit (a large dependency costs this on each edit).
• With libraries staged, a dependency added, removed or upgraded without a source edit (pip install -U, npm install, dotnet restore, a manifest or lockfile edit, fetching a missing Maven dependency) leaves the graph on the libraries it was built with until the next source edit.
• Compiled libraries are never cleaned up.