Query rangers cache in readonly mode only from within

Query rangers cache in readonly mode only from within

The change for 108356 allowed the cache to scan the dominator trees when
it was attempting a lookup rather than using the local value.  I
inadvertantly changed the externbal interface to also do this, so all
the GORI queries via range_on_edge of the cache could also do lookups.

This triggered a quadratic, possible expoential time increase when
the right conditions were presented. That being a cascading series of
recomputaions on outgoing edge calucaltions that at then searched the dom tree
instead of being a simple calcualtion using whats easily available.

The fix is to use the internal API within the cache rather than the
extrenal one that GORI uses.   This leaves GORI computations to be
resovled in linear time.

	PR tree-optimization/108687
	gcc/
	* gimple-range-cache.cc (ranger_cache::range_on_edge): Revert
	back to RFD_NONE mode for calculations.
	(ranger_cache::propagate_cache): Call the internal edge range API
	with RFD_READ_ONLY instead of changing the external routine.