Add RobotoFlex into AOSP system image

Cherry picked I8324c16fa8c392163e81fb9f4c21bba3343b6df0 to master due to b/286408867.

Code was merged via `-s ours` and is missing even though the sha exists on the target branch. Cherry pick is required to bring in the code.

Manually remove the "Merged in" directive to allow for downstream propagation.

(cherry picked from https://android-review.googlesource.com/q/commit:2872d3fa5b6923dbcfea99c4e5e7fd6bb3526f5f)

Bug: 235303866
Test: Manually done
Change-Id: I587161bd6fca5ac02a127a675ceab4f9203d2652