Problem: When an lsp client is stopped, the client will
only clear the diagnostics for the attached buffers but
not the unattached buffers.
Solution: Reset the diagnostics for the whole namespace rather than
for only the attached buffers.
(cherry picked from commit 025c874415)
Co-authored-by: crwebb85 <51029315+crwebb85@users.noreply.github.com>