The rest of the code base was already migrated last year in
https://crrev.com/c/1631409. In the API we have to be more careful to
not break embedders. According to the standard there is no semantic
difference between typedef and using ([decl.typedef#2]):
  A typedef-name can also be introduced by an alias-declaration. The
  identifier following the using keyword becomes a typedef-name and the
  optional attribute-specifier-seq following the identifier appertains
  to that typedef-name. Such a typedef-name has the same semantics as if
  it were introduced by the typedef specifier.

Thus this CL replaces all typedefs in include/v8.h by the equivalent
using declaration. This improves readability, especially for function
pointer types.

R=ulan@chromium.org
CC=leszeks@chromium.org

Bug: v8:11074
Change-Id: Id917b6aa5c8cd289c60bda5da1e3667e747936e7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2563880
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71719}