Introduce selectClasspathResources(Set) in DiscoverySelectors and deprecate selectClasspathResource(Set) #4873
Description
Overview
While working on #4868, I realized that we accidentally left of the "s" in the name of selectClasspathResource(Set) in DiscoverySelectors.
It should rather be called selectClasspathResources(Set) (plural), analogous to selectClasspathRoots() and selectModules().
Since selectClasspathResource(Set) was introduced in JUnit Platform 1.12, we need to leave it in place for the time being but in a @Deprecated state.