Fix for sketches script usage in checker options

Reduced blocking timeouts in the UI to 250ms and full block to 5000ms.

Fix for nested lambda tooltips not showing if they were generic
functions.

Refactored some common symbol parsing code so it can be reused rather
than copied.
@dsyme Its actually duplicated here too:
https://github.com/fsharp/FSharp.Compiler.Service/blob/master/src/fsharp/vs/ServiceDeclarations.fs#L47

I wonder if we should reuse/expose the `dataTipSpinWaitTime ` function or `mFSharp_ToolTipSpinWaitTime` environment variable?