This adds a little cache for debugging code, including stepping code.
Especially in stepping, we are currently repeatedly recompiling the same
function, because whenever we pause (after every step) we clear
stepping, only to reinstantiate it if the user continues stepping.
Especially in source-level stepping this is wasteful, because stepping
over a single line of C++ code can execute hundreds or thousands of
steps in wasm.

R=thibaudm@chromium.org

Bug: chromium:1172299
Change-Id: Id59a26cc67a5bf4a2d3cf6b1e8f14a8b1c73712c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2732015Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73162}