Provide relevant configuration for user when error occurred

[h9jiang]

This is a feature request derived from golang/vscode-go#3906

When an error occurred, the vscode-go extension normally inform the user by a notification. Normally, those notification have very limited information about the source of the issue, specifically, which setting is causing this issue.

Embedding such information in the notification message or in the go output channel could help user figure out which setting is causing this issue.

In addition, we could also report information by WorkspaceConfiguration.Inspect. This VSCode api gives us more visibility of how the settings is configured this way. When retrieving settings, we should still use WorkspaceConfiguration.Get which did all the merge and consolidation for us. But when an error happens, we can retrospectively inspect that setting and tell user those detail.