Moving these members:

   CHARSET_INFO *cs;
   const MY_UCA_WEIGHT_LEVEL *level;

from my_uca_scanner to a new separate structure my_uca_scanner_param.

Rationale:

During a comparison of two strings these members were initialized two times
(one time for every string).

After the change these members initialized only one time inside
a shared instance of my_uca_scanner_param, and the instance is
shared between two scanners (its const address is passed as new a parameter
to the underlying scanner functions).

This change gives a slight performance improvement (~5%).