Use basic code intel while language server hasn't returned a result

[felixfbecker]

While packages are still installing, we could show the basic-code-intel result if the language server couldn't find one (not just if no server is configured).
For hover and references we can replace the content/list once the real result is in.
For definition, we can always use a small timeout after which code intel is used.

@chrismwendt wdyt?

[chrismwendt]

(continuing from https://github.com/sourcegraph/sourcegraph-typescript/pull/140/files#r270624520)

Complaints were filed against the race() behavior in https://sourcegraph.slack.com/archives/C07KZF47K/p1553879931025500, so I reverted it in sourcegraph/sourcegraph-go#58

I might implement progressive-refinement behavior and put it behind a feature flag to gather feedback sourcegraph/sourcegraph-go#57 (comment), but it might be met with complaints similar to the race() behavior. I'm curious if you're optimistic about it.

[chrismwendt]

Closing because:

• Falling back reduces confidence in code intelligence for people who expect the language server's results https://sourcegraph.slack.com/archives/C07KZF47K/p1553879931025500
• Falling back would make it more difficult to troubleshoot language server setup issues such as https://sourcegraph.slack.com/archives/C0W2E592M/p1554110783001800