[ST-0015] Swift Testing image attachments (Windows) (#2940)

* [WIP] Swift Testing image attachments (Windows)

* Update NNNN-image-attachments-in-swift-testing-windows.md

Add pitch link

* Add another link to ST-0014.

* Update tools integration blurb

* Assign number (ST-0015) to image attachments on Windows proposal and adjust header fields

* Fill in my name as review manager

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Co-authored-by: Stuart Montgomery <[email protected]>

Author: grynspan