Update and Remove should optimize on identity matches

`Update` item operations provide a way to select items and set metadata on them.

When another item is used as selection (e.g. ``), MSBuild compares all items from the operation item type (Foo) with all items from the referenced item type (Bar) and updates the intersection. This results in N^2 runtime.

However, when the operation item type is the same as the referenced item type (e.g. ``) MSBuild could optimize and iterate over the items only once.

Suggested by @dsplaisted who found this is slow when there are many items in a self referencing update: https://github.com/Microsoft/msbuild/issues/2238#issuecomment-315937074

Optimizations:
- [x] self referencing Updates can short circuit matching altogether
- [x] extend the optimization in Update to all item operations that use matching (for now only Remove)
- [ ] add a lookup dictionary to ItemExpressionFragment such that operations that need to do matching hit the lookup instead of looping through all the ItemExpressionFragment items