[FEATURE] Use new TypoScript and TSConfig files extension

It was decided to use .typoscript and .tsconfig
The patch renames the files and adds little BC layer which allows
you to include TypoScript files using old (.txt) file extension.

Resolves: #81686
Releases: master
Change-Id: Id6784e4f573e2e0b060f37d241c07216ac5678e1
Reviewed-on: https://review.typo3.org/57083


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>