[InteractionRegions] Remove the RSS soft link and move to an SPI header
<rdar://problem/105775731>
Pull request: https://github.com/WebKit/WebKit/pull/16136
Committed 266363@main (5cc3d396317e): <https://commits.webkit.org/266363@main> Reviewed commits have been landed. Closing PR #16136 and removing active labels.