#376: rename virtual serialize macros

[cz4rs]

fixes #376

Adds magistrate_ version of the macros and deprecates the old checkpoint_ ones.

Since it's impossible to deprecate a macro on its own, I am using a helper (constexpr) function + a static_assert combo to generate warnings. You can see gtest doing a similiar thing here.

[cz4rs]

Example deprecation message from PR tests with vt job:

/vt/src/vt/runtime/component/diagnostic_value_base.h:72:3: warning: 'checkpoint_virtual_serialize_root_is_deprecated' is deprecated: checkpoint_virtual_serialize_root is deprecated, please use magistrate_virtual_serialize_root [-Wdeprecated-declarations]
  checkpoint_virtual_serialize_root()
  ^
/build/checkpoint/install/include/checkpoint/dispatch/vrt/base.h:60:17: note: expanded from macro 'checkpoint_virtual_serialize_root'
  static_assert(checkpoint_virtual_serialize_root_is_deprecated()); \
                ^
/build/checkpoint/install/include/checkpoint/dispatch/vrt/base.h:53:3: note: 'checkpoint_virtual_serialize_root_is_deprecated' has been explicitly marked deprecated here
[[deprecated("checkpoint_virtual_serialize_root is deprecated,"
  ^

[cwschilly]

Example deprecation message from PR tests with vt job:

/vt/src/vt/runtime/component/diagnostic_value_base.h:72:3: warning: 'checkpoint_virtual_serialize_root_is_deprecated' is deprecated: checkpoint_virtual_serialize_root is deprecated, please use magistrate_virtual_serialize_root [-Wdeprecated-declarations]
...

I don't fully understand this warning message. Why is checkpoint_virtual_serialize_root_is_deprecated deprecated?

[cz4rs]

I don't fully understand this warning message. Why is checkpoint_virtual_serialize_root_is_deprecated deprecated?

You cannot deprecate the macro itself, so I'm using this constexpr function to generate a warning. There's probably a couple of possibilities here, this one is inspired by gtest.

edit: Improved the PR description too.