LSIF improvements

Created by: sqs

I went through the process of setting up LSIF for one of my open-source Go repositories (https://github.com/sqs/rego) and ran into several problems and points of friction. The PRs above contain my fixes for them.

See commits and related PRs:

• https://github.com/sourcegraph/about/pull/418
• https://github.com/sourcegraph/sourcegraph-typescript/pull/284
• https://github.com/sourcegraph/sourcegraph-go/pull/107
• https://github.com/sourcegraph/sourcegraph-basic-code-intel/pull/177
• https://github.com/sourcegraph/lsif-upload-action/pull/5
• https://github.com/sourcegraph/src-cli/pull/68
• https://github.com/sourcegraph/lsif-upload-action/pull/6
• https://github.com/sourcegraph/lsif-upload-action/pull/7
• https://github.com/sourcegraph/lsif-upload-action/pull/8
• https://github.com/sourcegraph/sourcegraph/issues/6977