x/tools/gopls: release version v0.9.0

[dle8]

This issue tracks progress toward releasing gopls@v0.9.0

• merge master into gopls-release-branch.0.9
• update hard-coded version
• update go.mod/go.sum (remove x/tools replace, update x/tools version)
• tag gopls/v0.9.0-pre.1
• update Github milestone
• write release notes
• smoke test features
• tag gopls/v0.9.0

[gopherbot]

Change https://go.dev/cl/412815 mentions this issue: all: merge master (c353b05) into gopls-release-branch.0.9

[gopherbot]

Change https://go.dev/cl/412816 mentions this issue: internal/lsp/debug: update hard-coded version for v0.9.0

[gopherbot]

Change https://go.dev/cl/412819 mentions this issue: gopls: update go.mod for v0.9.0-pre.1

[gopherbot]

Change https://go.dev/cl/414497 mentions this issue: internal/lsp/debug: update hard-coded version for v0.9.0

[gopherbot]

Change https://go.dev/cl/414498 mentions this issue: gopls: update go.mod for v0.9.0-pre.2