Allow references to be marked as imprecise

[sqs]

There are many useful things that are like "references" but that are not precise: our current basic-code-intel extension, #981, cross-repo references that may take shortcuts to be imprecise, etc.

To support these without violating users' reasonable expectation that "references" means precise, it would be valuable to have a way to display imprecise references and communicate the imprecision clearly to the user.

Strawman ideas:

1. Extensions could mark individual reference results in a field on the result element that would cause the UI to display an "imprecise" or "best-effort" badge (possibly with an explanatory tooltip or label).
2. Extensions could contribute new panel tabs other than "References", such as "API matches (imprecise)" or "Text matches". Downside: the tab title would need to convey the imprecision, which could make it long and therefore weird-looking in the UI. (Related: External references UI #1172.)

cc @tsenart

[tsenart]

I like the first idea.

[sqs]

@francisschmaltz I'll just find a place to add a badge to these reference results (idea 1 above) unless you have any better ideas.

[francisschmaltz]

We should replace the repo badge with this icon if the match is from basic-code-intel:
https://materialdesignicons.com/icon/blur