[BUGFIX] TCA load regression in eid context

TCA refactoring in 6.1 misses an edge case:
Frontend index_ts loads TCA *after* eid is handled, so there is
no TCA loaded in eid context. Eid scripts that still need
TCA *should* call EidUtility::initTCA(), but some call instead
TSFE->includeTCA(). But includeTCA() is empty now and deprecated.

The patch adds a call to includeTCA() to load TCA, if
GLOBALS['TCA'] array is empty. This makes sure populating TCA
is done only once.

ext:caretaker_instance is affected by this, eg. test "Check
backend user accounts" needs TCA and fails without the patch.

Change-Id: Iaa70fe62e0eba9981e31379b853c968efe1d4cca
Resolves: #47993
Releases: 6.2, 6.1
Reviewed-on: https://review.typo3.org/20554
Reviewed-by: Markus Klein
Reviewed-by: Alexander Opitz
Reviewed-by: Stefan Neufeind
Tested-by: Alexander Opitz
Reviewed-by: Felix Kopp
Reviewed-by: Dmitry Dulepov
Tested-by: Markus Klein