Code intelligence tracking issue 3.12

Created by: chrismwendt

Theme Increase user confidence in code intelligence provided by LSIF and make setup easier.

Sourcegraph project roadmap

• Fall back to basic code intel because LSIF might be sparse https://github.com/sourcegraph/sourcegraph-basic-code-intel/pull/179
• Drop basic code intel results from files that have LSIF results https://github.com/sourcegraph/sourcegraph-basic-code-intel/pull/180
• Recognize more variable names in various languages https://github.com/sourcegraph/sourcegraph-basic-code-intel/pull/186
• RFC 89: Indicating precision levels of code intel in UI (Eric)
• Dart LSIF indexer https://github.com/sourcegraph/lsif-dart / https://github.com/sourcegraph/crossdart (Chris, Rijnard)