Set a proper type for string literals on ConstantColumn ctor
to fix the regression produced by MCOL-174.
Removed OPTIMIZER_SWITCH_EXISTS_TO_IN b/c MDB produces
unsupported optimization with it and CS couldn't create
ExistsFilter.
SH query execution migrated from SH::init() into create_SH().
There is a session variable columnstore_processing_handlers_fallback
that allows to fallback to DH, GBH if SH fails. DH now uses semantic
tree check for unsupported features to allow to fallback to GBH or
storage API.
Fixes GBH related bug when create_GBH() returns a handler for
queries with impossible WHERE/HAVING.
Fixed bug in FromSubquery::transform() where isUnion is set to true.
Enabled RTTI b/c server team enabled it for MDB.
Removed unused code supposed to be used with vtable.
The MariaDB handler API changed for write_row(). The 'buf' parameter is
now a 'const'. This meant that our implementation didn't match the
virtual call so ours was no longer called. This implemented the 'const'.
Renamed isInfiniDB() into isMCSTable
Changed getSelectPlan() to reuse it with derived and
other handler types.
Separate pushdown handlers methods and functions.
Removed vcxproj files from the source.
Added fix for MCOL-2166.
Merged with MCOL-2121
