This change adds a new abstract type Lazy<T> which can be used to
interoperate with CSA code that uses LazyNode. This new type has special
code-generation rules because its generated type is not TNode<...> but
std::function<TNode<...>()>. Torque code can do nothing with this type
except pass it around, but passing it to the CSA function RunLazy is an
easy way to execute the std::function and get back a normal value.
Torque code can also create Lazy<T> values using the intrinsic function
%MakeLazy, which takes the name of a macro as its first parameter,
followed by arguments to that macro which will be passed when the
LazyNode is evaluated. We use the macro's name because the language
doesn't support taking references to macros, and implementing such a
feature would be complicated.

Bug: v8:7793
Change-Id: I09120960e3492dd51be0d4c57e14ff3826b99262
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2701752
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72964}