x/tools/gopls: diagnostics only clear after diagnosticsDelay for edited files

[findleyr]

Reported by @heschi and @ShoshinNikita (in #57987 (comment)), https://go.dev/cl/477979 introduced a bug whereby diagnostics in the current package are not cleared until the diagnosticsDelay expired. Diagnostics should be cleared immediately upon edits.

Fix incoming.

[gopherbot]

Change https://go.dev/cl/484195 mentions this issue: gopls/internal/lsp: fix initial publication of diagnostics