Leaking clangd clients when multiple files per project are opened

[bddavis]

Setup:
Configure extension to enable Multi Project, with any Multi Project strategy.

Open one file in a project -> starts one clangd process.
Open a second file in the project -> starts a second clangd process.
Close either file -> both processes remain.
Close the other file -> one of the processes (the one started last) is stopped, but the rest remain.

With this one can leak an arbitrary number of these processes/clients per project.