Merge collation customization improvements

MySQL-5.6 introduced a few collation customization improvements:

1. Long contractions - reset to more than 2 characters
2. Long expansions - shift for a sequence of more than 2 characters
3. Contractions with expansions (a combination of N1 and N2)
4. Reset before
5. Long tailoring
6. Letters rather than escape sequences.
7. Quaternary difference
8. Abbreviated shift syntax:
9. Normal expansion syntax
10. Previous context
11. Previous context with expansion
12. Logical reset positions
13. More verbosity when reading character set definition file (Index.xml)
14. Special purpose commands and collation settings

These improvements allow to add more language specific collations.
This MDEV is to merge the new collation features.

Under terms of this task we'll also merge the following collations
introduced in MySQL-5.6:

• utf8_german2_ci
• utf8mb4_german2_ci
• ucs2_german2_ci
• utf16_german2_ci
• utf32_german2_ci