Feature: #65250 - TypoScript condition add GPmerged

See Issue #65250

Description

If one uses TypoScript condition with GP then the check is with GeneralUtility::_GP() which means that if I have GET variables beginning with an extbase plugin-namespace and POST variables with the same plugin-namespace, e.g. GET: tx_demo_demo[action]=detail POST: tx_demo_demo[name]=Foo then GeneralUtility::_GP('tx_demo_demo'), as intended, will only return the array of the POST variables for that namespace. However, that results in the issue that if you check for the GET variable the check will fail.

So, instead the check should use GeneralUtility::_GPmerged()

[globalVar = GPmerged:tx_demo|foo = 1]
page.90 = TEXT
page.90.value = DEMO
[global]