Reapplies f14cb494a3 (which was reverted in 2f08f8426c) with a fix for UB in
the ExecutorAddr::Unwrap::Unwrap constructor (which caused failures on some
bots).
The wrap/unwrap operations are applied to pointers after/before conversion to/from
raw addresses. They can be used to tag, untag, sign, or strip signing from
pointers. They currently default to 'rawPtr' (identity) on all platforms, but it
is expected that the default will be set based on the host architecture, e.g.
they would default to signing/stripping for arm64e.
In the common case of converting an ExecutorAddr to a function pointer type,
this eliminates the need for the '(*)' boilerplate to explicitly specify a
function pointer. E.g.:
auto *F = A.toPtr<int(*)()>();
can now be written as
auto *F = A.toPtr<int()>();
Lang Hames