Fall back to basic code intel if hover/def takes too long

Created by: chrismwendt

Sometimes it takes 10+ seconds for a hover to appear on moderately-sized repos (especially immediately after opening a file). A couple of examples:

• 8s to initial hover for TypeScript https://sourcegraph.com/github.com/sourcegraph/codeintellify@1936b9668f7f622f71d21670e224d1c2b9b84449/-/blob/src/hoverifier.ts#L455:82
• 11s to initial hover for Go https://sourcegraph.com/github.com/sourcegraph/sourcegraph@f5b050d5295224c8fd7bdff3b7cc2a2062de590e/-/blob/cmd/symbols/internal/symbols/parse.go#L66:35

This can be mitigated by falling back to basic code intel after a threshold amount of time elapses (e.g. 500ms).