Update and Remove should optimize on identity matches

[cdmihai]

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

When another item is used as selection (e.g. <Foo Update="@(Bar) Metadata="Value">), 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. <Foo Update="@(Foo) Metadata="Value">) 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: #2238 (comment)

Optimizations:

• self referencing Updates can short circuit matching altogether
• 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

[dsplaisted]

I was thinking that a more general solution would be to create a dictionary lookup if the ReferencedItem count of an ItemExpressionFragment was high enough. That way you wouldn't get n^2 runtime in situations where you have two different lists with a lot of items, such as <A Update="@(B)" />.

[dsplaisted]

Re-opening per comment: #5350 (review)