[BUGFIX] Escape dots of flexform field names

To make inline proper working in JS, the name of the field must be escaped
as it can contain dots.

Resolves: #78985
Releases: master, 7.6
Change-Id: I18c1d85906b9710c25b326b89e8104f3ea3c8a29
Reviewed-on: https://review.typo3.org/51014


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>