x/tools/gopls: go list error messages are too verbose/hard to interpret

[stamblerre]

This is an umbrella issue tracking our plans to parse and enhance the error messages from go list.

#41462 and #38383 reference a larger problem--some go list error messages are hard for users to understand and fix. They also often include the full arguments to the full go list invocation, which can often be confusing because they will include the workspace module or the -modfile flag.

We should try to parse and clean up the go list error messages as much as possible--and offer ways to fix the problem if possible.

/cc @jayconrod @bcmills @matloob in case they have input