shader: Rework varyings and implement passthrough geometry shaders

Put all varyings into a single std::bitset with helpers to access it.

Implement passthrough geometry shaders using host's.

src/shader_recompiler/profile.h

@@ -34,6 +34,7 @@ struct Profile {
     bool support_demote_to_helper_invocation{};
     bool support_int64_atomics{};
     bool support_derivative_control{};
+    bool support_geometry_shader_passthrough{};
     bool support_gl_nv_gpu_shader_5{};
     bool support_gl_amd_gpu_shader_half_float{};
     bool support_gl_texture_shadow_lod{};