extension: update gopls v0.18.0-pre.1 settings

This is an automated CL which updates the gopls version and settings.

For golang/go#71607

Change-Id: I7478642c2bdbd47c9a961054c5d46843312be100
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/647717
Reviewed-by: Alan Donovan <[email protected]>
Auto-Submit: Gopher Robot <[email protected]>
Reviewed-by: Hongxiang Jiang <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
kokoro-CI: kokoro <[email protected]>

Author: gopherbot