Perf Measurements, improvements

[DonJayamanne]

Opening Notebooks

• Start time - when we get a request to provide contents to VS Code
• End Time A - when we get the event that a notebook was opened
• End Time B - when we get a message from kernel.js loaded in Renderer (today we do this in resolve, to keep IPYWidgets kernel ready)

Fetching Kernels

• Today when we fetch kernels, its slow, can be very slow on some OS
• We can easily cache this & find the preferred kernel from the cache
• If we fine the preferred kernel from cache & its valid, then we can use that
• We can always start off the kernel fetch in the background as well
• If we have metadata & have cached kernels, and the kernel exists in the cache, just check if the kernel is valid (file exists/interpreter exists), that should be sufficient (faster than loading all interpreters & searching the fs).

[DonJayamanne]

Not required anymore