[FEATURE] Add support for XLIFF 2.0 format

[bmgrieger]

TYPO3 14 encourages to use XLIFF 2.0 for new projects. This PR adds support for the new format while still preserving support for XLIFF 1.2

[rrrapha]

Hi @bmgrieger
Thanks a lot fot this! It seems to work fine at first glance.

Here are some questions:

Would you mind making version 2.0 the default? I would prefer something like this for this option:

# cat=Basic; type=options[2.0 (default)=default,1.2=1.2]; label=XLIFF version for saving files (both versions are read)
xliffVersion = default

Similarly, I would use the following names for the template files:
For 2.0: Empty.xlf and Xliff.html
For 1.2: Empty1.2.xlf and Xliff1.2.html

Multiple segment tags per unit are not supported at the moment. Is this a problem or does Typo3 not support this?

[bmgrieger]

@rrrapha I switched to XLIFF 2.0 as default. I can't answer your question regarding multiple segments. I just ignored it for now for simplicity reasons and used the example files from TYPO3 documentation for orientation.