video_core: add workarounds to enable GLES support

video_core: shorten GetGLSLVersionString

video_core: make GLES version and extensions consistent

video_core: move some logic to LoadShader

video_core: deduplicate fragment shader precision specifier

src/video_core/video_core.cpp

@@ -7,6 +7,7 @@
 #include "core/settings.h"
 #include "video_core/pica.h"
 #include "video_core/renderer_base.h"
+#include "video_core/renderer_opengl/gl_vars.h"
 #include "video_core/renderer_opengl/renderer_opengl.h"
 #include "video_core/video_core.h"
 
@@ -36,6 +37,8 @@ Core::System::ResultStatus Init(EmuWindow& emu_window, Memory::MemorySystem& mem
     g_memory = &memory;
     Pica::Init();
 
+    OpenGL::GLES = Settings::values.use_gles;
+
     g_renderer = std::make_unique<OpenGL::RendererOpenGL>(emu_window);
     Core::System::ResultStatus result = g_renderer->Init();