SplitPane resizing broken in 35.15.1

[mattcosta7]

Description

In 35.15.1 we shipped #2606 which overrides the 'overflow' to auto for the split pane view, and avoids the explict width we should be setting for resizing.

https://github.com/primer/react/pull/2606/files#diff-e4049ccb37961f4fa30e007dfb5b91b6c42dfa7cc680f0d287857577d2bf8d2fR175

Steps to reproduce

Try to resize the split pane in the latest version, notice it wont resize

Version

v35.15.1

Browser

No response