[BUGIFX] Missing update wizard for RTE file links

File links made inside a RTE-enabled field are currently not
migrated to FAL references. This patch adds such an update
wizard.

Resolves: #49233
Releases: 6.1, 6.2
Change-Id: I12b6d9da87b734c0a9d5f884d5067e3c9b08efc3
Reviewed-on: https://review.typo3.org/22134
Reviewed-by: Francois Suter
Tested-by: Francois Suter