Feature: #22439 - Allow nested GET-params in config.linkVars

See forge#22439

Description

TypoScript setting config.linkVars configures which parameters should be passed on with links in TYPO3. It is now possible to specify nested GET parameters there.

Example:

config.linkVars = L(0-2),tracking|green(0-5)
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With the above configuration the following example GET parameters will be kept:

&L=1&tracking[green]=3

But a get parameter like tracking[blue] will not be kept.

The value constraint in round brackets works in the same way as for not nested GET parameters.