Port member initialization from constructor to declaration (C++11)

Using `clang-tidy`'s `modernize-use-default-member-init` check and
manual review of the changes, and some extra manual changes that
`clang-tidy` failed to do.

Also went manually through all of `core` to find occurrences that
`clang-tidy` couldn't handle, especially all initializations done
in a constructor without using initializer lists.

modules/bullet/godot_ray_world_algorithm.cpp

@@ -52,7 +52,6 @@ GodotRayWorldAlgorithm::GodotRayWorldAlgorithm(const btDiscreteDynamicsWorld *wo
 		btActivatingCollisionAlgorithm(ci, body0Wrap, body1Wrap),
 		m_world(world),
 		m_manifoldPtr(mf),
-		m_ownManifold(false),
 		m_isSwapped(isSwapped) {}
 
 GodotRayWorldAlgorithm::~GodotRayWorldAlgorithm() {