gl_shader_disk_cache: Default ShaderDiskCacheOpenGL's destructor in the cpp file

Given the disk shader cache contains non-trivial types, we should
default it in the cpp file in order to prevent inlining of the
complex destruction logic.

src/video_core/renderer_opengl/gl_shader_disk_cache.cpp

@@ -107,6 +107,8 @@ bool ShaderDiskCacheRaw::Save(FileUtil::IOFile& file) const {
 ShaderDiskCacheOpenGL::ShaderDiskCacheOpenGL(Core::System& system)
     : system{system}, precompiled_cache_virtual_file_offset{0} {}
 
+ShaderDiskCacheOpenGL::~ShaderDiskCacheOpenGL() = default;
+
 std::optional<std::pair<std::vector<ShaderDiskCacheRaw>, std::vector<ShaderDiskCacheUsage>>>
 ShaderDiskCacheOpenGL::LoadTransferable() {
     // Skip games without title id

src/video_core/renderer_opengl/gl_shader_disk_cache.h

@@ -162,6 +162,7 @@ struct ShaderDiskCacheDump {
 class ShaderDiskCacheOpenGL {
 public:
     explicit ShaderDiskCacheOpenGL(Core::System& system);
+    ~ShaderDiskCacheOpenGL();
 
     /// Loads transferable cache. If file has a old version or on failure, it deletes the file.
     std::optional<std::pair<std::vector<ShaderDiskCacheRaw>, std::vector<ShaderDiskCacheUsage>>>