Merge "Include <sstream> explicitly, and don't rely on the implicit include via <complex>." am: 46241a925a am: 1128de5640

Original change: https://android-review.googlesource.com/c/platform/external/eigen/+/1657199

Change-Id: Icba6fac3953fd4d3c54c10ac28428b79b4b9d8e4