Update iconloaderlib min_sdk_version to 26. am: e5430492 am: 235562ce am: 80b5920b am: 1d3bacd8

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/libs/systemui/+/15602014

Change-Id: Ibe24650dd8614b7897cd307c7609d342d0626600