Memory leak

[NatElkins]

Making an issue here at the request of @Krzysztof-Cieslak . When using Ionide on a large solution (60+ projects), there is a memory leak.

Details originally in this issue: https://github.com/dotnet/diagnostics/issues/669

The leaky process from that original issue was

nat               7949  31.2  4.4 40483832 735964   ??  R     9:02AM 121:41.58 dotnet /Users/nat/.vscode/extensions/ionide.ionide-fsharp-4.3.2/bin_netcore/fsautocomplete.backgroundservices.dll 7911

which, while I was not actively using Ionide (it was just open in the background), eventually consumed 21GB of memory before I closed it.

I haven't been able to get it down to a minimal repro, but I'll report back if I do.