[BUGFIX] TSConfig for fields with a dot in the name does not work

This patch enables the use of double quotes in TypoScript setup paths.
Thus, for example, can Extbase field names be separated using quotes in
TSConfig.

Example:

TCEFORM.tt_content.pi_flexform.myext_myplugin.sDEF {
  "settings.fieldOne".config.type = text
  "settings.fieldTwo" = foo
}

Fixes: #29461
Releases: 6.1
Change-Id: Idf30faff9c45c662b2c2f976aeda5cc407e9610a
Reviewed-on: https://review.typo3.org/7711
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Eric Chavaillaz
Tested-by: Eric Chavaillaz
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn