[Python] PEP 750 Template Strings (t-string)

[zufuliu]

https://peps.python.org/pep-0750/
https://discuss.python.org/t/pep750-template-strings-new-updates/71594

A simple implementation is just treated it as PEP 701 f-string (issue #150) with new prefixes (t, tr, rt, case insensitive).

https://peps.python.org/pep-0750/#relationship-with-other-peps

Python introduced f-strings in Python 3.6 with PEP 498. The grammar was then formalized in PEP 701 which also lifted some restrictions. This PEP is based on PEP 701.

cc @jpe

[nyamatongwe]

For symmetry likely needs another property lexer.python.strings.t to enable, similar to lexer.python.strings.f enabling f-strings.

[zufuliu]

Python 3.14 (with Unicode 16.0) was released.
https://www.python.org/downloads/release/python-3140/

[nyamatongwe]

#328 addresses this.