Cache instances from call hierarchy provider

[colin-grant-work]

What it does

As part of #10310, it was found that Theia does not satisfy the expectations of VSCode CLangD (or any other language client based on vscode-languageclient) because we do not guarantee that the plugin will receive the same instances of CallHierarchyItems that it creates when calls are made.

This PR addresses that problem by caching call hierarchy items received from plugins and retrieving them when passing them back into the plugin.

In addition, it moves some way to addressing #10528, but with a twist. Since call hierarchy items are now being cached, there's need for a signal to clear the cache, and the return from CallHierarchyAdapter.prepareCallHierarchy is now a CallHierarchySession that includes a disposable to dispose of the cache. That isn't part of the API available to plugins, so the VSCode references view never disposes of its sessions (as far as I can tell, CallHierarchySessions are never disposed of in VSCode), but our internal view does know when to dispose of its sessions, so I have left the view in, but adjusted the types to eliminate our purely internal types in favor of close mirrors of the plugin types.

How to test

1. Install the latest CLangD plugin

To install the CLangD plugin, add this line to the .theiaPlugins field of the repo's package.json:

"vscode-clangd": "https://open-vsx.org/api/llvm-vs-code-extensions/vscode-clangd/0.1.13/file/llvm-vs-code-extensions.vscode-clangd-0.1.13.vsix"

2. Open the examples/cpp-debug-workspace from the Theia CPP Extensions repo
3. Open a.cpp
4. Use Calls: Show Call Hierarchy on one of the functions there other than main.
5. You should get results, and you should be able to expand those results.
6. Call hierarchy for languages like TS, etc. should continue to work as before in both references view and internal view.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

I confirmed that it works well 👍

• the code looks good.
• confirmed that call-hierarchy from out custom view works well using clangd.
• confirmed that show call hierarchy (plugin side) works well as well.