Move range allocator code to value-range-storage.*

Move range allocator code to value-range-storage.*

Now that vrange_storage is in its own file, I think it's prudent to
move all the vrange allocator code there since it's all related.
The users of value-range.h do not need to know the implementation
details of the storage facilities.

Tested and benchmarked on x86-64 Linux.

gcc/ChangeLog:

	* gimple-range-cache.cc: Include value-range-storage.h.
	* gimple-range-cache.h (class block_range_cache): Add "class" to
	m_range_allocator.
	* gimple-range-edge.cc
	(gimple_outgoing_range::gimple_outgoing_range): Allocate allocator.
	(gimple_outgoing_range::~gimple_outgoing_range): Free allocator.
	(gimple_outgoing_range::calc_switch_ranges): Dereference allocator.
	* gimple-range-edge.h: Add "class" to m_range_allocator.
	* gimple-range-infer.cc
	(infer_range_manager::infer_range_manager): Allocate allocator.
	(infer_range_manager::~infer_range_manager): Free allocator.
	(infer_range_manager::get_nonzero): Dereference allocator.
	(infer_range_manager::add_range): Same.
	* gimple-range-infer.h (class vrange_allocator): Add "class" to
	m_range_allocator.
	* value-range-storage.h (class vrange_allocator): Move from
	value-range.h.
	(class obstack_vrange_allocator): Same.
	(class ggc_vrange_allocator): Same.
	(vrange_allocator::alloc_vrange): Same.
	(vrange_allocator::alloc_irange): Same.
	* value-range.h (class vrange_allocator): Move to value-range-storage.h.
	(class obstack_vrange_allocator): Same.
	(class ggc_vrange_allocator): Same.