HPCC-9481 CSV record definition auto discovery 

Add
- implementation for CSV record structure discover
- new parameter to signal CSV file contains field definition in first row
- new parameter handling to WU enviromnet
- new parameter handling to DFUPlus
- new parameter handling to ECL SprayDelimited(), fSprayDelimited(), SprayVariable() and fSprayVariable().
- new C++ interface function to File plugin.

Signed-off-by: Attila Vamos <attila.vamos@gmail.com>