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.cpp

@@ -12,6 +12,10 @@
 
 namespace FileSys {
 
+ProgramMetadata::ProgramMetadata() = default;
+
+ProgramMetadata::~ProgramMetadata() = default;
+
 Loader::ResultStatus ProgramMetadata::Load(VirtualFile file) {
     std::size_t total_size = static_cast<std::size_t>(file->GetSize());
     if (total_size < sizeof(Header))