entry: Mark Entry::from_parts_1_1() as unsafe

`Entry` is the only struct marking some Vulkan API calls as safe, as
their soundness can be trivially upheld.  This however relies on
`vkGetInstanceProcAddr` returning a sound function pointer, which is not
something we can guarantee when the user passes us function pointers via
`Entry::from_parts_1_1()` instead: hence mark this new constructor as
`unsafe` to uphold this contract.

Related discussion chain: #748 (comment)

Changelog.md

@@ -16,7 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added `VK_EXT_shader_object` device extension (#732)
 - Added missing `Device::get_device_queue2()` wrapper (#736)
 - Exposed `FramebufferCreateInfo::attachment_count()` builder for `vk::FramebufferCreateFlags::IMAGELESS` (#747)
-- Allow building `Entry`/`Instance`/`Device` from handle+fns (#748)
+- Allow building `Entry`/`Instance`/`Device` from handle+fns (see their `from_parts_x_x()` associated functions) (#748)
 
 ### Changed
 

ash/src/entry.rs

@@ -155,7 +155,7 @@ impl Entry {
     }
 
     #[inline]
-    pub fn from_parts_1_1(
+    pub unsafe fn from_parts_1_1(
         static_fn: vk::StaticFn,
         entry_fn_1_0: vk::EntryFnV1_0,
         entry_fn_1_1: vk::EntryFnV1_1,