Refactor MetaspaceShared::use_full_module_graph()

The function bool MetaspaceShared::use_full_module_graph() has two meanings:

- Should we dump the full module graph when doing -Xshare:dump
- Should we load the full module graph when loading a shared archive

This overloaded meaning can lead to strange code:

https://github.com/openjdk/jdk/blob/fe0ccdf5f8a5559a608d2e2cd2b6aecbe245c5ec/src/hotspot/share/oops/instanceKlass.cpp#L2693-L2702

void InstanceKlass::init_shared_package_entry() {
#if !INCLUDE_CDS_JAVA_HEAP
  _package_entry = nullptr;
#else
  if (!MetaspaceShared::use_full_module_graph()) {
    _package_entry = nullptr;
  } else if (CDSConfig::is_dumping_dynamic_archive()) {
    if (!MetaspaceShared::is_in_shared_metaspace(_package_entry)) {
      _package_entry = nullptr;
    }
  } else {

Here: MetaspaceShared::use_full_module_graph() could mean "we are loading the FMG from the base archive, but we are writing into the dynamic archive, which doesn't have an FMG"

We should split this function to two variants:

CDSConfig::is_dumping_full_module_graph()
CDSConfig::is_loading_full_module_graph()