This commit adds the `glFramebufferTextureMultisampleMultiviewOVR`
function, enabling MSAA to work in conjunction with the multiview
extension.
The function's declaration is present in the latest main branch of the
Khronos GLES2 API headers. While directly pulling these updated headers
is the ideal approach, it would necessitate a significant reorganization
of Filament's current header file structure and incorporate more files
than currently needed.
To minimize immediate changes and limit scope, this change adopts
only the necessary function declaration by copying it directly.
BUGS=[417311684]
If the shared osmesa lib is not found, then we assume that the
library has been compile-time linked via the linker. This is to
accommodate build frameworks where compile-time linking is
preferred.
Previously, we linked against libOSMesa through the linker and
then used dlopen to link against libGL. This is not how libOSMesa
is intended to be used. Instead, we use dlopen on libOSMesa
(via bluegl), which then will map the correct GL methods for us,
and for the OSMesa functions, we also map those functions
from libOSMesa (instead of relying on compile-time linker).
I have disabled building SDL with headless EGL, because
SDL_config_minimal.h doesn't work with EGL, and I don't know how to
implement a an SDL config that would work with EGL.
I have verified that this works in a separate project, and that it
compiles in this project.
```
$ ./build.sh -e release
$ find ./out/ -name "*EGL*"
./out/cmake-release/filament/backend/CMakeFiles/backend.dir/src/opengl/platforms/PlatformEGL.cpp.o
./out/cmake-release/filament/backend/CMakeFiles/backend.dir/src/opengl/platforms/PlatformEGLHeadless.cpp.o
./out/cmake-release/libs/bluegl/CMakeFiles/bluegl.dir/src/BlueGLLinuxEGL.cpp.o
```
Some clients need to link against both Filament and OpenGL. This can lead to symbol clashes under certain circumstances. As a fix, prefix all of our `bluegl` symbols with `bluegl_`. Previously we made this naming change for Windows, but now we'll do it on all platforms for simplicity.
- add darwin-aarch64 support to bluegl
- remove all aarch64 conditions in our cmakefiles, the architecture
is better handled in the source files (to allow fat binaries later)
