internal: new shared_ptr and weak_ptr implementation (#5883)

moves std::shared_ptrs to a new implementation

Advantages:
- you can dereference a weak_ptr directly. This will obviously segfault on a nullptr deref if it's expired.
   - this is useful to avoid the .lock() hell where we are 100% sure the pointer _should_ be valid. (and if it isn't, it should throw.)
- weak_ptrs are still valid while the SP is being destroyed.
   - reasoning: while an object (e.g. CWindow) is being destroyed, its `weak_ptr self` should be accessible (the sp is still alive, and so is CWindow), but it's not because by stl it's already expired (to prevent resurrection)
   - this impl solves it differently. w_p is expired, but can still be dereferenced and used. Creating `s_p`s is not possible anymore, though.
   - this is useful in destructors and callbacks.

src/desktop/WLSurface.cpp

@@ -175,9 +175,9 @@ std::optional<CBox> CWLSurface::getSurfaceBoxGlobal() {
         return {};
 
     if (!m_pWindowOwner.expired())
-        return m_pWindowOwner.lock()->getWindowMainSurfaceBox();
+        return m_pWindowOwner->getWindowMainSurfaceBox();
     if (!m_pLayerOwner.expired())
-        return m_pLayerOwner.lock()->geometry;
+        return m_pLayerOwner->geometry;
     if (m_pPopupOwner)
         return CBox{m_pPopupOwner->coordsGlobal(), m_pPopupOwner->size()};
     if (m_pSubsurfaceOwner)
@@ -186,7 +186,7 @@ std::optional<CBox> CWLSurface::getSurfaceBoxGlobal() {
     return {};
 }
 
-void CWLSurface::appendConstraint(std::weak_ptr<CPointerConstraint> constraint) {
+void CWLSurface::appendConstraint(WP<CPointerConstraint> constraint) {
     m_pConstraint = constraint;
 }
 
@@ -194,7 +194,7 @@ void CWLSurface::onCommit() {
     ;
 }
 
-std::shared_ptr<CPointerConstraint> CWLSurface::constraint() {
+SP<CPointerConstraint> CWLSurface::constraint() {
     return m_pConstraint.lock();
 }