x/tools/gopls: release version v0.8.3

[findleyr]

We plan to release gopls@v0.8.3 next week to pick up support for staticcheck@v0.3.0, which supports generics (see also #52159).

Tentative plan: tag a prerelease today and let it soak until next week.

• merge master into gopls-release-branch.0.8
• update hard-coded version
• update go.mod/go.sum (remove x/tools replace, update x/tools version)
• tag gopls/v0.8.3-pre.1
• update Github milestone
• write release notes
• smoke test features
• tag gopls/v0.8.3

[gopherbot]

Change https://go.dev/cl/398814 mentions this issue: all: merge master (7f10777) into gopls-release-branch.0.8

[gopherbot]

Change https://go.dev/cl/398815 mentions this issue: internal/lsp/debug: update hard-coded version for v0.8.3

[gopherbot]

Change https://go.dev/cl/398816 mentions this issue: gopls: update go.mod for v0.8.3