ItemFragment.CreateFileMatcher allocating 2.6% of solution-wide design-time build just getting directory name

[davkean]

This is creating a copy of the same string (project directory) over and over again:

[davkean]

Also consuming 0.6% of CPU time:

[davkean]

In one trace from a major partner - this is allocating 60 MB opening their solution.

[davkean]

Here's another trace where this is 5.5% of all allocations opening the solution:

[davkean]

Out for review.