Make sure that the current bytecode's size is taken into account when
updating the interrupt budget (on jumps and returns), so that jumps are
not "free" from an interrupt point of view.

Also clarifies, corrects and cleans up the interrupt budget update for
returns.

Bug: v8:6238
Change-Id: I1099d53a232fab4c1fcc91115baee610bfbce1d6
Reviewed-on: https://chromium-review.googlesource.com/472809Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44533}