Contract for a Gradle "convention object" that acts as a handler for what I call a virtual directory mapping,
injecting a virtual directory named 'antlr' into the project's various source
sets. Its implementation gets pushed onto the DynamicObjectAware portion of the
source set under the name 'antlr'.
Configures the Antlr source for this set. The given closure is used to configure the SourceDirectorySet (see
getAntlr()) which contains the Antlr source.
Parameters:
configureClosure - The closure to use to configure the Antlr source.