file-sys: Default heavy-weight class destructors in the cpp file

Several classes have a lot of non-trivial members within them, or don't
but likely should have the destructor defaulted in the cpp file for
future-proofing/being more friendly to forward declarations.

Leaving the destructor unspecified allows the compiler to inline the
destruction code all over the place, which is generally undesirable from
a code bloat perspective.

src/core/file_sys/program_metadata.h

@@ -36,6 +36,9 @@ enum class ProgramFilePermission : u64 {
  */
 class ProgramMetadata {
 public:
+    ProgramMetadata();
+    ~ProgramMetadata();
+
     Loader::ResultStatus Load(VirtualFile file);
 
     bool Is64BitProgram() const;