shader/memory_util: Deduplicate code

Deduplicate code shared between vk_pipeline_cache and gl_shader_cache as
well as shader decoder code.

While we are at it, fix a bug in gl_shader_cache where compute shaders
had an start offset of a stage shader.

src/video_core/shader/shader_ir.h

@@ -18,6 +18,7 @@
 #include "video_core/engines/shader_header.h"
 #include "video_core/shader/ast.h"
 #include "video_core/shader/compiler_settings.h"
+#include "video_core/shader/memory_util.h"
 #include "video_core/shader/node.h"
 #include "video_core/shader/registry.h"
 
@@ -25,8 +26,6 @@ namespace VideoCommon::Shader {
 
 struct ShaderBlock;
 
-using ProgramCode = std::vector<u64>;
-
 constexpr u32 MAX_PROGRAM_LENGTH = 0x1000;
 
 class ConstBuffer {