Allow Buffer classes to add new abstract methods

The buffer classes don't have a public constructor. It should be fine to
add new abstract methods.

Commands to update these files:
m update-api && m droid
cp out/soong/.intermediates/libcore/art.module.public.api.stubs.source/android_common/metalava/last_released_baseline.txt prebuilts/sdk/34/public/api/art-incompatibilities.txt
m update-api && m droid
cp out/soong/.intermediates/frameworks/base/api/frameworks-base-api-current-compat/gen/updated-baseline.txt prebuilts/sdk/34/public/api/android-incompatibilities.txt

Bug: 240254046
Test: m droid
Merged-In: Ia6d726b30406054f0fce2d6a16ec1fc945d7206e
Change-Id: Ia6d726b30406054f0fce2d6a16ec1fc945d7206e
2 files changed