Previously, we would simulate disk-based diagnostics finishing after
saving a buffer. However, the language server may produce diagnostics
right after emitting the event, causing the diagnostics status bar item
to not reflect the latest state of the buffer.
With this change, we will instead simulate disk-based diagnostics finishing
after 1s after saving the buffer (only for language servers that
don't have the concept of disk-based diagnostics, such as TypeScript). This
ensures we always reflect the latest state and doesn't cause the UI to flicker
as a result of the LSP sending us diagnostics after every input.
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