Choice of wrong binary from "Choose Go Environment" breaks the extension permanently

[hyangah]

0.18.0 introduced the file explorer option with which users can select the go binary to use.
It does some basic check on the binary (i.e. whether the version subcommand is accepted), accepts the user's selection, and stores the info in the workspace Memento. If the binary is an invalid go binary, this leaves the extension. In that state, Go: Choose Go Environment command fails - users even can't clear the bad value from the workspace Memento.

How to reproduce

• Select the file explorer from the option
• Select a binary that has 'version' subcommand, e.g. gopls or dlv or a simple shell script.
• Reload the window

Current workaround

• Reinstall 'code'.

What we want

• We shouldn't fail miserably like this - at least users should be able to reset the memento.
• Enhance validation logic running after users select the go binary.

[gopherbot]

Change https://golang.org/cl/267898 mentions this issue: src/goEnvironmentStatus: correctly interpret the chosen go path