x/tools/gopls: modernizer for sync.OnceValues

[adonovan]

Proposal Details

Some complex uses of sync.Once can be much simplified using OnceValues; see
https://go.dev/cl/728860 for example. Let's add a modernizer that recognizes the pattern.

[gabyhelp]

Related Issues

• x/tools/gopls/internal/analysis/modernize: add modernizer for WaitGroup.Go #73059 (closed)
• net/http: use sync.OnceFunc, sync.OnceValue #69634 (closed)
• x/tools/gopls/internal/analysis: add "modernizer" analyzers #70815 (closed)
• x/tools/go/analysis/passes/modernize: publish #75266 (closed)
• x/tools/gopls/internal/analysis/modernize: add pass to use reflect.TypeAssert #75422

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}