Add memory_resource diagnostics interface

[thirtytwobits]

It's common for applications to maintain metrics for custom memory_resources. We should define a common interface that uses rtti allowing generic code to see if a given resource supports diagnostics and to obtain them.

Difficulties here include how to go from non-rtti pmr::memory_resource to the diagnostics interface type.

[pavel-kirienko]

Difficulties here include how to go from non-rtti pmr::memory_resource to the diagnostics interface type.

This use case is supported in cetl::rtti via specializations of type_id_getter():

CETL/include/cetl/rtti.hpp

Lines 79 to 88 in 88fd7a3

	/// The type ID getter for the given type.
	/// This helper is provided for regularity; it returns the same value as \c T::_get_type_id_().
	/// The type shall satisfy \ref cetl::has_type_id.
	/// Specialize this getter to add RTTI support to types where it is not possible to define a static method
	/// (e.g., builtins, pointers, third-party classes, etc).
	template <typename T>
	constexpr type_id type_id_getter() noexcept
	{
	return T::_get_type_id_();
	}

So we just specialize it for pmr::memory_resource and we're done