Update signal to remove a connection when disconnected

[jslee02]

The current Signal design doesn't clean up disconnected connections until the signal calls the registered slots:

dart/dart/common/detail/Signal.hpp

Lines 120 to 141 in 3f76766

	template <typename _Res, typename... _ArgTypes, template <class> class Combiner>
	template <typename... ArgTypes>
	_Res Signal<_Res(_ArgTypes...), Combiner>::raise(ArgTypes&&... _args)
	{
	std::vector<ResultType> res(mConnectionBodies.size());
	auto resIt = res.begin();
	for (auto itr = mConnectionBodies.begin(); itr != mConnectionBodies.end();)
	{
	if ((*itr)->isConnected())
	{
	*(resIt++) = (*itr)->getSlot()(std::forward<ArgTypes>(_args)...);
	++itr;
	}
	else
	{
	mConnectionBodies.erase(itr++);
	}
	}
	return Combiner<ResultType>::process(res.begin(), resIt);
	}

or cleanupConnection() is explicitly called. This could lead to large memory consumption if we make many connections and disconnect them before emitting the signal or don't use cleanupConnection() in a right time.

This PR Signal to remove the disconnected connections when it's disconnected. This change keeps the backward compatibility because none of the public API isn't being changed.

---

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[codecov]

Codecov Report

Merging #1462 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1462      +/-   ##
==========================================
- Coverage   58.21%   58.20%   -0.01%     
==========================================
  Files         412      412              
  Lines       29928    29911      -17     
==========================================
- Hits        17423    17411      -12     
+ Misses      12505    12500       -5     

Impacted Files	Coverage Δ
dart/common/detail/ConnectionBody.cpp	100.00% <ø> (ø)
dart/common/Signal.cpp	81.48% <100.00%> (-2.90%)	⬇️
dart/common/detail/ConnectionBody.hpp	100.00% <100.00%> (ø)
dart/common/detail/Signal.hpp	100.00% <100.00%> (+1.75%)	⬆️
dart/collision/detail/UnorderedPairs.hpp	90.00% <0.00%> (-5.00%)	⬇️
dart/dynamics/EulerJoint.cpp	73.00% <0.00%> (+3.68%)	⬆️