Merge "Add kotlinpoet and rxjava2 prebuilts." am: 2a1038fb2a am: 71f81b7034

Original change: https://android-review.googlesource.com/c/platform/prebuilts/tools/+/1783940

Change-Id: I2d0fdf7e636a64bdda45b9a01563d8f0ca06e1f4