[TASK] Verify @-sign is a valid TypoScript identifier

ext:form tends to use email addresses as
TypoScript identifier. The old TS parser
did not deal with this, the new one does.

The patch adds tests to the TS tokenizer
to verify this works.

Resolves: #101732
Related: #97816
Related: #92902
Releases: main, 12.4
Change-Id: If1ee1dfe9c136316e67c05c4f1c1740018c1fd60
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80620


Tested-by: Stefan B�rk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Stefan B�rk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>