Request for review: 8007762: Rename a bunch of methods in size policy across collectors

[Tao Mao]

8007762: Rename a bunch of methods in size policy across collectors
https://jbs.oracle.com/bugs/browse/JDK-8007762

webrev:
http://cr.openjdk.java.net/~tamao/8007762/webrev.01/

changeset:
The motivation of this change is associated with CR 7098155 
(https://jbs.oracle.com/bugs/browse/JDK-7098155). For this, we need to 
split compute_generations_free_space into two routines (one for 
compute_eden_space_size and the other for compute_old_gen_free_space) in 
order to save some overhead when we want to compute only one of the two 
(JBS 8007763).

To unify the naming, a bunch of routines are renamed here.
(1) rename compute_generation_free_space() to 
compute_generations_free_space() to reflect its complexity
(2) compute_*:
       compute_survivor_space_size_and_threshold()
       compute_generations_free_space() = compute_eden_space_size() + 
compute_old_gen_free_space()
(3) resize_*_gen:
       resize_young_gen()
       resize_old_gen()

testing:
purely renaming; passed JPRT