x/tools/gopls: deprecate the "allowImplicitNetworkAccess" setting

[findleyr]

Gopls has long had an experimental setting to allow network access for all go command invocations: "allowImplicitNetworkAccess".

We should not have settings that affect low level behavior like this, as such settings are inevitably insufficiently tested and hard to maintain. Gopls should work well with its default decisions about allowing network access.

This issue tracks officially deprecating this setting in gopls@v0.16.0, to be removed in gopls@v0.17.0 (as we've been doing for these sorts of settings).

[gopherbot]

Change https://go.dev/cl/579437 mentions this issue: gopls/internal/settings: deprecate "allowImplicitNetworkAccess"