Also cleanup variable class size calculation for 'new'
statements as well as spread-based indexed field
initialization in Torque rather than in hand-written
ImplementationVisitor code. This is done with new
%-intrinsics. With this change, %-intrinsics can also
have bodies, in which case they are treated as macros.

Bug: v8:7793
Change-Id: I012d57166761688747eb683cb618263e8d0953db
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1554695
Commit-Queue: Daniel Clifford <danno@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61585}