Changes

Wayland: Fix leak of surface scaling objects
 (commit: 42dc1ff)

Null: Add Vulkan 'window' surface creation

This adds support for Vulkan 'window' surface creation on the Null
platform via the VK_EXT_headless_surface extension, where available.

Tested with MoltenVK.
 (commit: 860c8ef)

Null: Add limited EGL context creation on Mesa

This provides very limited support for context creation via EGL on the
Null platform.  It supports Unix-like systems with a version of Mesa
that provides EGL_MESA_platform_surfaceless.

Even then, the actual framebuffer provided is not resized along with the
'window'.  That will hopefully change once context and framebuffer
creation are separated, but this commit should at least allow more
applications than before to run on the Null platform.
 (commit: 738dd6f)

Fix missing assertions for native access functions
 (commit: 38ec7ab)

Place assertions for handles after init check

This lets automated testing check that GLFW_NOT_INITIALIZED is emitted
for every public function.
 (commit: 68dcea0)

Allow C99 booleans
 (commit: 072f660)

Wayland: Fix segfault when there is no seat

Bug encountered running on a headless instance of Weston.

Fixes #2517
 (commit: 3573c5a)

EGL: Allow native access with defaults on Wayland

The intent of enforcing GLFW_EGL_CONTEXT_API for EGL native access
functions was to ensure that the application had requested the same
context creation API at window creation time that it then attempted
native access for.

With the 3.4 ABI this both isn't true anymore, as a single binary may
have multiple meanings of GLFW_NATIVE_CONTEXT_API, and is no longer
necessary, since glfwGetPlatform provides enough information to
disambiguate even without knowing what GLFW_PLATFORM was set to.

This all leaves the requirement that the context creation API be
GLFW_EGL_CONTEXT_API as just an unnecessary annoyance.

Fixes #2518
 (commit: 228e582)