gl_shader_manager: Move using statement into the cpp file

Avoids introducing Maxwell3D into the namespace for everything that
includes the header.

src/video_core/renderer_opengl/gl_shader_manager.cpp

@@ -6,6 +6,8 @@
 
 namespace OpenGL::GLShader {
 
+using Tegra::Engines::Maxwell3D;
+
 void MaxwellUniformData::SetFromRegs(const Maxwell3D& maxwell, std::size_t shader_stage) {
     const auto& regs = maxwell.regs;
     const auto& state = maxwell.state;
@@ -16,7 +18,7 @@ void MaxwellUniformData::SetFromRegs(const Maxwell3D& maxwell, std::size_t shade
 
     u32 func = static_cast<u32>(regs.alpha_test_func);
     // Normalize the gl variants of opCompare to be the same as the normal variants
-    u32 op_gl_variant_base = static_cast<u32>(Tegra::Engines::Maxwell3D::Regs::ComparisonOp::Never);
+    const u32 op_gl_variant_base = static_cast<u32>(Maxwell3D::Regs::ComparisonOp::Never);
     if (func >= op_gl_variant_base) {
         func = func - op_gl_variant_base + 1U;
     }

src/video_core/renderer_opengl/gl_shader_manager.h

@@ -12,14 +12,12 @@
 
 namespace OpenGL::GLShader {
 
-using Tegra::Engines::Maxwell3D;
-
 /// Uniform structure for the Uniform Buffer Object, all vectors must be 16-byte aligned
 /// @note Always keep a vec4 at the end. The GL spec is not clear whether the alignment at
 ///       the end of a uniform block is included in UNIFORM_BLOCK_DATA_SIZE or not.
 ///       Not following that rule will cause problems on some AMD drivers.
 struct MaxwellUniformData {
-    void SetFromRegs(const Maxwell3D& maxwell, std::size_t shader_stage);
+    void SetFromRegs(const Tegra::Engines::Maxwell3D& maxwell, std::size_t shader_stage);
 
     alignas(16) GLvec4 viewport_flip;
     struct alignas(16) {