Feature request: Include `P4est.jl` as dependency

[jmark]

T8code.jl respectively t8code_jll.jl come with their own shared libraries of p4est and libsc. In order to avoid
namespace collisions the bindings for these libraries are not exported to the global namespace as is done for the
t8code bindings. This means, fully qualified names are necessary in order to use p4est_* and sc_* routines.

However, it would be more elegant to use the same routines from P4est.jl instead. But, with the current configuration
the shared libraries from different packages do not properly "see each other" and do not communicate in therms of
adress spaces which is vital for memory management.

This should be investigated.

The questions is: How does the mechanism of loading shared libraries from different packages into the same adress space work? Especially, on different platforms such as Linux, MacOS and Windows.