fix(exthost/#3009): Call '$release*' APIs to clean-up extension host cache

[bryphe]

Issue: There is a memory leak in our completion items, signature help, and codelens via the extension host - may be responsible for the SIGABRT described in #3009 (as this can occur when the JS heap is out of memory).

Defect: The extension host adds a layer on top of the language server protocol, to serve as a cache for several language features - this helps performance when resolving items. However, this caching layer relies on the client to notify it when the items are no longer in use, so they can be cleaned up. Onivim was missing this release step.

Fix: Bake in the call to release in all the relevant subscriptions. This involves picking up the cacheId which wasn't wired up in some places (like codelens), setting up the release* API, and passing it back on conclusion of the subscription.

To test this fix - I flipped the Cache.enableDebugLogging flag in the extension host and initiated several completions. Before this fix, it's obvious the caches were simply growing endlessly:

CompletionItem cache size — 1
CompletionItem cache size — 1
CompletionItem cache size — 2
CompletionItem cache size — 2
SignatureHelp cache size — 1
CompletionItem cache size — 3
CompletionItem cache size — 3
CompletionItem cache size — 4
CompletionItem cache size — 4
SignatureHelp cache size — 2
...
CompletionItem cache size — 15
CompletionItem cache size — 15
CompletionItem cache size — 16
CompletionItem cache size — 16
CompletionItem cache size — 17
CompletionItem cache size — 17
SignatureHelp cache size — 8
CompletionItem cache size — 18
CompletionItem cache size — 18
CompletionItem cache size — 19
CompletionItem cache size — 19

After this fix, though, we can observe that the cache gets cleaned:

CompletionItem cache size — 1
CompletionItem cache size — 1
CompletionItem cache size — 0
CompletionItem cache size — 0
CompletionItem cache size — 1
CompletionItem cache size — 1
CompletionItem cache size — 0
CompletionItem cache size — 0
SignatureHelp cache size — 1
SignatureHelp cache size — 0

...
CompletionItem cache size — 0
CompletionItem cache size — 0
SignatureHelp cache size — 1
SignatureHelp cache size — 0

Related #3009
Related #1058