tools: replace `go-outline` with `gopls`

[hyangah]

go-outline is no longer used for outline view when language server is enabled.
However, it's still being used by GoDocumentSymbolProvider that is used for

• generate tests: goGenerateTests.ts
• references codelens: goReferencesCodelens.ts
• run test/benchmark codelenses: goRuntestCodelens.ts

They can be replaced with gopls's implementation LanguageClient.getFeatures("textDocument/documentSymbol") or with a direct invocation of vscode.commands.executeCommand('vscode.executeDocumentSymbolProvider', ...).

One difference between the gopls's document symbol provider and GoDocumentSymbolProvider is gopls version doesn't provide the file's package name info, so we need a different way to find the package name if the info is necessary. See golang/go#40514.

[qdm12]

Any update on this one? Can we drop go-outline already if we use gopls today? Or is it still needed? Thanks!

[mihaitodor]

Would be great to see this one fixed. go-outline doesn't seem to be actively maintained and VS Code has a hard time installing it in some cases: ramya-rao-a/go-outline#15