Split vr's generate_jni() target into two

This should prevent the default classloader from being cached for the vr
split, which then causes incorrect values when installing the DFM on T+
devices.

Bug: b/258453540
Change-Id: Idd2753aa6fd4539dce9949a5289e99d5c3c90eca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4062308


Reviewed-by: Clark DuVall <cduvall@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Owners-Override: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1076505}