... at function start. Otherwise we run into a position mismatch:
In a non-flooded function, we add the function-entry breakpoint (for
"hook on function call") with the position of the first opcode.
In the flooded function though, we skip that special breakpoint because
we will stop at the first instruction anyway. But then the first
instruction is non-breakable, so we don't actually emit a breakpoint for
it.
Hence during OSR we do not find a corresponding position in the new
code.

This CL fixes this by postponing the function-entry breakpoint until the
first breakable opcode is found, and only emits it if that position does
not have a breakpoint anyway.
This way, we can also move the handling for function-entry breakpoints
from {StartFunctionBody} to {EmitDebuggingInfo}, where it fits much
better.

R=thibaudm@chromium.org

Bug: chromium:1137710
Change-Id: Idfa658fa0897cca89ba5ee3066cd414f68864d06
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2474774Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70529}