Merge "Add hidl-gen to build tools" am: 3fcde0a898 am: b62a14a1e6 am: 69406c2a7b

Original change: https://android-review.googlesource.com/c/platform/prebuilts/build-tools/+/1421851

Change-Id: I39403b9fe2153382d3263337fb6f3c910d4cf11b