LibGfx+LibWeb: Add support for Vulkan EGL contexts

[ADKaster]

This almost works(?) but fails like so to actually open the WebGL context on https://twgljs.org/examples/primitives.html:

INFO: EGL ERROR: : Internal Vulkan error (-1000158000): Unknown vulkan error code, in ../../src/libANGLE/renderer/vulkan/vk_helpers.cpp, initExternal:6342.
VERIFICATION FAILED: egl_image != EGL_NO_IMAGE_KHR at /home/andrew/ladybird-org/ladybird-browser/Libraries/LibWeb/WebGL/OpenGLContext.cpp:209

Where -1000158000 is VK_ERROR_INVALID_EXTERNAL_HANDLE.

In order to test this, I needed to get my own local checkout of angle and set LD_LIBRARY_PATH. The vcpkg provided build segfaults in eglInitialize on my AMD GPU system.

The steps for that are as follows:

1. clone depot_tools git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
2. I added a function to temporarily prepend depot_tools to my path to my bashrc:

with_depot() {
  PATH=/home/andrew/ladybird-org/depot_tools:$PATH $@
}

exact path varies

3. clone angle using gclient:

cd ..
mkdir angle
cd angle
with_depot fetch angle

4. configure angle to use vulkan and skip a few heavy deps:

with_depot gn gen out/Debug
with_depot gn args out/Debug
<paste the following args.gn into the editor>

args.gn

# Set build arguments here. See `gn help buildargs`.

angle_build_tests = false
angle_enable_swiftshader = false
angle_enable_vulkan = true
angle_enable_wgpu = false
angle_expose_non_conformant_extensions_and_versions = true

5. build angle

with_depot ninja -C out/Debug

6. Run ladybird with custom angle

LD_LIBRARY_PATH=$PWD/../angle/out/Debug ./Build/release/bin/Ladybird https://twgljs.org/examples/primitives.html