Close processes before spawning new ones

[ramya-rao-a]

Features that depend on Go tools spawn a new process for every new request made.
When the tools get slow (for any which reason) this ends up generating multiple processes for the same tool.

This is more prominent for tools that back features like hover and auto-completion.

This issue is to track the possibility of closing older processes for these features when new ones are spawned.

[ramya-rao-a]

This has been done. The only remaining feature that does not do this yet is the auto-completions which is tracked in #1272