WL#1025: More fulltext control functions

1) We need a simple way to take a look at build in STOPWORD list, as well as the
one currently active. This is good for example for filtering stopwords from user
input.  This is to be done as part of INFORMATION_SCHEMA or if we will be too
slow with it SHOW STOPWORDS; and SHOW BUILDIN STOPWORDS; can be added.

2) Another useful idea was once on the list:

======================
- a function which returns a table, which can tell me, what can be
  searched.

E.g SHOW MATCH(table.index) AGAINST('hugobla hugo bla');

 word      count     rows     stopword   autostopword   score wscore
 hugobla      2        2        no         no             10      1
 hugo        10        6        no         no              8      1
 bla          0        0        no         yes             0      1
======================


(it's raw idea as it was on the list. Actual output layout will be,
of course, different)

see also BUG#32138