Change Handle representation to be non-nullable so that Option<Handle> is FFI-safe

[necauqua]

While I rewrote the OUT pointers in UEFI methods to use MaybeUninit (which actually looks very clean and logical) to avoid ever having null handles, the reason for the repr change is so that whenever an UEFI method accepts a handle - by the docs it can be optional or not, and this can be expressed by just having either Handle or Option<Handle> in the fn-pointer args, which is very clean and removes the need for null handles (Handle::unitialized()) to ever exist on Rust side.

I spent a night debugging my impls of (dis)connect_controller (that I will make a PR for too at some point) only to realize that I automatically assumed that whatever I did in the PR was already there ¯_(ツ)_/¯

[nicholasbishop]

Looks like a good change to me, left a couple comments. Please also rebase the fixup commits into the first commit.

[necauqua]

Also I've just realised that an identical change can be made for Event as well, there are optional (nullable) event parameters in some functions in some protocols, I'll need to look into that I guess

[necauqua]

Oh wow on ut/doctest stage it does not know that such feature exists, no idea how to fix it besides reverting back to using ManuallyDrop and stuff

[nicholasbishop]

Ah that is confusing. I think it's because that feature is part of alloc but not core, since Vec isn't in core. But those tests are running with all feature disabled, so the alloc crate isn't available.

To fix, gate the feature behind exts:

diff --git a/src/lib.rs b/src/lib.rs
index b12602b..035aee3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -23,13 +23,12 @@
 //! For example, a PC with no network card might not contain a network driver,
 //! therefore all the network protocols will be unavailable.
 
-#![cfg_attr(feature = "exts", feature(allocator_api, alloc_layout_extra))]
+#![cfg_attr(feature = "exts", feature(allocator_api, alloc_layout_extra, vec_into_raw_parts))]
 #![feature(auto_traits)]
 #![feature(control_flow_enum)]
 #![feature(try_trait_v2)]
 #![feature(abi_efiapi)]
 #![feature(negative_impls)]
-#![feature(vec_into_raw_parts)]
 #![no_std]
 // Enable some additional warnings and lints.
 #![warn(missing_docs, unused)]

[nicholasbishop]

Please rebase against latest master to resolve the conflict in boot.rs, and then I think it'll be good to merge.

[necauqua]

Right, totally forgot about the other MR

[nicholasbishop]

Thanks, merging now.