Improve index selection on functional index for RBO

Repro from: Marco Greco , Bingjie Miao 

CREATE INDEX `ix1` ON `default`(c1);

CREATE INDEX `ix2` ON `default`(upper(c1)) ;

EXPLAIN select raw count(1) as count from  default  as b  where upper(c1) like 'abc_xyz_%'

EXPLAIN select b.* from  default  as b  where upper(c1) like 'abc%';

We randomly pick the index because both has same sargable keys.

If sargable keys same try to see if we can further explore (some of the options) before random selection.

• If key pos depends on other give preference
• If span is not full span (not superset) give preference.