gccrs: Make early name resolver inherit from default one

gccrs: Make early name resolver inherit from default one

Many visit functions in the early name resolver are just plain old
traversal visit functions like the ones from the default visitor.

gcc/rust/ChangeLog:

	* resolve/rust-early-name-resolver.cc (EarlyNameResolver::resolve_generic_args):
	Move function.
	(EarlyNameResolver::resolve_qualified_path_type): Likewise.
	(EarlyNameResolver::visit): Add a top level visit function for crate
	and remove duplicated code.
	* resolve/rust-early-name-resolver.h (class EarlyNameResolver): Update
	overriden function list.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>