Previously, DefaultResourceLoader instances were created using the
default constructor. This causes the resource loader to capture the
TCCL that was in place at that time. This can lead to a class loader
leak if the resource loader is referenced directly or indirectly from
a static field of a class loaded by a different class loader.

This commit updates the creation of DefaultResourceLoader instances
in main code so that the resource load will use the class loader of
the creating class. In almost all cases this will be the same class
loader as was the thread context class loader that was being captured
so the change in behavior is minimal. Crucially, it will still address
the situation where the TCCL was different.

Note the DevTools' ApplicationContextResourceLoader has been updated
to explicitly use the TCCL. This ensures that it uses the restart
class loader which is required for DevTools to function correctly.

Fixes gh-20900