Investigate why we are disposing of so many things on startup

When debugging, I noticed that `dispose` ends up being called a lot while VS Code is starting up. This is suspicious because it suggests that we may be doing work that is either not needed or doing work that later needs to be re-done. There are valid reasons this can happen to, but I see around 2500 calls to our global `dispose` function on startup with a single editor open (which does not track places where `.dispose` is called directly on an object) Here's some example code where this happens: https://github.com/microsoft/vscode/blob/36fdf6b697cba431beb6e391b5a8c5f3606975a1/src/vs/workbench/contrib/debug/browser/debugToolBar.ts#L317 This function is called twice on startup (even though the debug toolbar is not visible in the editor). This means that the work that the first call does is likely pointless, as the second call disposes of it and then does the work over again --- With some very basic profiling, I see 2500 calls to the global `dispose()` function on startup, which cumulatively take around 40ms. Of these, 1200 actually seem to dispose of something (this filters out the cases where `dispose` is called on an empty array or empty iterable) Even though this is a small direct performance cost, this is still something interesting to investigate because: - The profiling above only measures the time spent in the `dispose` implementations. It does not include the cost of computing the values that are then disposed off. I suspect this is more significant - Looking at these calls can be a good way to track down work that should be deferred. In the debug toolbar example above, it helped reveal that we're updating the debug toolbar on startup even though the debug toolbar is not visible