Creates a ClearableLinker from a function creating a Linker.
Creates a ClearableLinker from a function creating a Linker.
Every time clear() is called, a new Linker is obtained from the
newLinker function to ensure that all the previous state is discarded.
newLinker must returned a new, independent instance of Linker every
time it is called.
If batchMode is true, the returned ClearableLinker clears itself
after every invocation of link.