NavigableItemCache & NavigateToItem -> FSharp.Editing

[cloudRoutine]

• NavigableItemCache
• NavigateToItem

The Cache implementation needs to be changed so that it's built around projects instead of solutions to avoid the duplication of projects that are shared by multiple solutions.

The ServiceProvider and usage of the DTE can be removed, instead the cache can be constructed using a collection of project paths

A SolutionEvent manager will need to be implemented in Logic to control the behavior of the cache in core. Additionally it should respond to project load and unload events and adjust the cache accordingly

Eventually cacheFilePath will need a platform specific location to store the elements per project

NavigateToItem's index processing and search should be moved to FSharp.Editing

Code Located @
https://github.com/fsprojects/VisualFSharpPowerTools/blob/master/src/FSharp.Editing.VisualStudio/Navigation/NavigableItemCache.fs