fix(mobile): cronet buffer overflow on compressed thumbnails (#28439)

CronetImageFetcher sized the response buffer from Content-Length, which is
the compressed wire size. Cronet auto-decompresses gzip/br responses and
writes decompressed bytes into the buffer, exceeding it and throwing
IllegalArgumentException: ByteBuffer is already full on the next read. Use
the growable path; Content-Length becomes an initial alloc hint only,
capped at 128 MB so an untrusted server can't overflow Int.MAX_VALUE or
OOM us upfront. Reuse Cronet's ByteBuffer between reads when no grow is
needed.