Hover actions from extensions, better handling of multiple def providers

[sqs]

The goal of this PR is to make basic-code-intel an awesome experience when you need go-to-definition, hovers, and find-references when browsing code in any language with no configuration. That means that the initial experience of site admins and users will be much better, because they get to see code intelligence with much less setup required.

This incorporates the codeintellify PR sourcegraph/codeintellify#70. That PR makes it so that codeintellify (which implements our hover tooltip) supports custom actions, instead of hardcoding "Go to definition" and "Find references".

This commit makes the web app (and TODO soon the browser extension) make use of that, so that:

1. The "Go to definition" and "Find references" actions work in the same way in the web app and browser extension as all other action buttons. This means those actions are no longer hard-coded in a separate library.
2. These buttons are selectively displayed in a smarter way based on (e.g.) whether there are any registered definition or reference providers for the current document. This fixes the issue where both buttons were always shown if there was a hover, even if the client app knew they would not return anything.
3. The buttons can do smarter things, like opening up the definition panel if there are multiple definitions (instead of just jumping to the 1st definition).
4. Extensions can add their own actions to the hover, such as "Find implementations", "Show history" (eg when a func, or calls to a func, were added/removed in Git history), "Show authors", "Show users", "Show stack traces", etc.

(I initially began implementing this so that basic-code-intel could add "Go to definition (fuzzy)" to the hover using (4), but I think that the improvements in (2) and (3) actually make that unnecessary for basic-code-intel. (It's still important to prioritize precise definitions in the panel; that will come soon.) See sourcegraph/sourcegraph-basic-code-intel#9 for the basic-code-intel changes that make use of this new behavior. (Note that there are no new extension APIs added in this PR, just improved handling of what already exists.))

TODOs before merging:

• Update the browser extension impl code to use this
• Add more tests to actions.test.ts
• Fix issue where the input rev is discarded and the absolute commit ID SHA is used
• Add back logTelemetryEvent for code intel action logging - make HoverOverlay record it

[dadlerj]

If you prefer to change naming scheme, can we do it more comprehensively in a separate step, and stick with the old ones for now? Don't want this to look like a list that any ext authors can add to.

Perhaps we add a new category in the future for non-Sourcegraph extension usage tracking/displaying.

[sqs]

It’s going to start tracking all actions run by extensions btw.

But these actions added here are builtin and not from extensions. For marking them actions as code intel, I either need to change the action ID in hover/actions.ts or here (and for technical reasons we need to distinguish between the preloaded j2d and non-preloaded, so we’d need add another entry here anyway). Ok with you now?

[dadlerj]

K, I'd love to understand (and discuss) the full vision for telemetry from extensions in the future. Would like to avoid some of VS Code's mistakes.

For now this is fine of course. Can we delete the pre-existing predefined event names (like "GoToDefClicked") in this PR though if codeintellify is already updated?

[sqs]

Yep, will delete the preexisting event names.

Check out https://github.com/sourcegraph/sourcegraph/pull/1559/files#diff-34372db774cd5ac796ed38d6db567d70 for what I was thinking around extension telemetry and leave your thoughts there. 👍

[codecov-io]

Codecov Report

Merging #1313 into master will increase coverage by 0.4%.
The diff coverage is 89.48%.

Impacted Files	Coverage Δ
shared/src/api/client/services/registry.ts	100% <ø> (ø)	⬆️
shared/src/actions/ActionItem.tsx	81.92% <ø> (ø)	⬆️
shared/src/api/protocol/contribution.ts	100% <100%> (ø)	⬆️
shared/src/hover/helpers.ts	60.86% <60.86%> (ø)
shared/src/hover/HoverOverlay.tsx	75.86% <75.86%> (ø)
shared/src/hover/actions.ts	91.89% <91.89%> (ø)
shared/src/hover/HoverOverlay.test.tsx	96.15% <96.15%> (ø)
shared/src/hover/actions.test.ts	96.96% <96.96%> (ø)
... and 4 more