Activation refactor

[efritz]

This PR cleans up the init code after sourcegraph/code-intel-extensions#198.

This removes all LSIF and search-based logic and instead delegates to the activateCodeIntel function, passing it only the language-server specific logic.

This PR will be followed by a major cleanup.

[chrismwendt]

I got an error with "typescript.serverUrl": ""

Passing undefined to the lspProviders argument when that's unset might do the trick.

[efritz]

Passing undefined to the lspProviders argument when that's unset might do the trick.

Updated.

[chrismwendt]

I verified the hover/def/ref behavior with/without LSIF/LSP remains unchanged (same as sourcegraph/sourcegraph-go#117 (review))

[felixfbecker]

Note that before, you could change the config during a session and it would be considered. Now it seems the config is read only once during activation. I think this could cause problems in particular in the browser extension, where extensions are run in the background page and are not necessarily re-activated just because the page got reloaded.

[efritz]

Ah you're right - I missed that. We used to check on each function invocation. I'll update the new API to support doing this dynamically.

[efritz]

See sourcegraph/code-intel-extensions#198 (comment).