Restructure BitBufferWriter to write to uninitialized memory

Specifically, when writing into previously unwritten byte, set remaining
bits to zero instead of preserving them.

Remove 'ConsumeBits' from the public api to discourage skipping writing
bits, instead add and use function to zero next bits.

memory sanitizer analalyse memory access at byte level and thus
complains when uninitialized bits are read and preserved.

Bug: b/473210445
Change-Id: I409ee14cf6844a78a4e438bbf18ed7b16cab687a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/441062
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#46626}