It turns out that most LEBs are rather small (especially when used for
locals). This CL adds a fast path for single-byte LEBs which is supposed
to be inlined into callers. The more expensive slow path is then
explicitly outlined to avoid excessive binary size growth.

R=thibaudm@chromium.org

Change-Id: I0dcdf597b9be3055acc2b878b6bee3fa21839758
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2449974
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70408}