[TASK] dbal: Add support for ALTER TABLE ADD/DROP KEY

Add support for creating and removing indices to DBAL. The SQL is
generated using the respective ADOdb methods, so adding/removing
PRIMARY keys is not possible.

MySQL prefix lengths will be removed from columns in an index
definition unless the DBMS specifically enables support for this
feature. To ensure that index columns get properly quoted by
ADOdb the field names need to be wrapped in backticks.

Due to the common requirement that index names must be unique within a
database/schema the requested index name will be prepended with a
unique table name identifier.

Resolves: #67445
Resolves: #67531
Releases: master
Change-Id: I274be8df3078867309dde0d5771853c67903719d
Reviewed-on: http://review.typo3.org/40397


Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Tested-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>