This fixes the bug with hover tooltips appearing multiple times.
Turns out everytime we receive the `CreateLanguageServer` message we'd
add a new adapter but only have a single server running for all of them.
And we send a `CreateLanguageServer` message everytime you open a
buffer.
What this does is to only add a new adapter if it hasn't already been
registered, which is also what we do locally.
Release Notes:
- N/A
Thorsten Ball
90a12f5564