add smart optimizer usage of full text index for like operator

Add a variable like

optimizer_convert_like_to ft

with default = 0.

If set to 1

set optimizer_convert_like_to ft = 1

1.
Analyze, if query have conditions, which likely cause a full scan
like

tag LIKE '%aaaa%' OR LIKE '%bbbb%' 

2
Check, if the column has a full text index.

If 1. + 2. true ,
the query use full text index like "match against" syntax.

This can improve application, where changing the queries is difficult like snow