TYPO3 Core

Problem:
The processing of GET/POST variables in TypoScript does not have a consistent naming scheme:
- TS conditions use GP for GET/POST vars in globalVar and globalString.
- TS getText uses GPvar
User might be confused by an unconsistent naming scheme.

Solution:
Since t3lib_div::GPvar is deprecated, GP should be also used in getText. For backward compatibility, leave gpvar as is and add gp as an alternative. Add a hint in TSref to use gp instead of gpvar in getText.

We'd also have to change TSref chapter on conditions:

IMPORTANT NOTE ON globalVar and globalString:
(...)
Caring about this means that you would get values like HTTP_HOST by getenv(), you would retrieve GET/POST values with t3lib_div::GPvar().
(...)
(issue imported from #M10357)