Write the official `cpython` documentation for t-strings

[koxudaxi]

We should write the offical document for https://docs.python.org/3/library/

• Document string.templatelib in the Library reference section
• Find all mentions of f-strings in the current documentation and decide whether there should also be a reference to t-strings
• Add AST nodes to the ast docs
• Glossary
• Add new t-string roles to lexical-analysis.rst section with the _f-strings role and make sure it covers t-strings appropriately.
• Lexical analysis, adjust f-strings section (probably keep one section and talk about f-string and t-string syntax in it, since it's so closely tied)
• Add BUILD_INTERPOLATION and BUILD_TEMPLATE to the dis docs, probably somewhere near BUILD_TUPLE
• Lexical analysis, adjust String and Bytes literals section (Pending changes in this PR by @encukou .)
• Update the Template strings section of Doc/library/string.rst to clarify that this is unrelated to t-strings (it's $-strings)
• A section after the f-strings part of the tutorial where perhaps we show writing a function. I'm 50-50 on this (the cookbook might be enough.)

---

This can be a follow-on PR, but probably shouldn't be part of the first PR?:

• Consider building a "Python string formatting cookbook" that explains when you might use each of Python's increasingly many formatting features. (One question we got asked a lot at PyCon was: "are f-strings deprecated"?)

[davepeck]

Obsoleted all of these, moved to issue body.

@lysnikolaou @AA-Turner would also love your input here.

[lysnikolaou]

During the PyCon sprints, we edited @davepeck's comment above to include more places that need to be adjusted.

A couple of comments:

Find all mentions of f-strings in the current documentation and decide whether there should also be a reference to t-strings

Agreed that we should try and change some places where f-strings are mentioned (some are listed below this bullet point). To be honest, I wouldn't give that much emphasis to adjusting all the occurences. It's perfectly fine for places in the docs to talk about f-strings without mentioning t-strings.

Consider building a "Python string formatting cookbook" that explains when you might use each of Python's increasingly many formatting features. (One question we got asked a lot at PyCon was: "are f-strings deprecated"?)

I agree that a "cookbook" is a good idea. We could probably add a "t-strings HOWTO" in the section with all the HOWTOs.

[blaisep]

cross-posting a related thread from the mothership: https://discuss.python.org/t/t-stringd-doc-pep-750-and-amish-barn-raising/93654

[encukou]

Dibs on Lexical analysis, then!

If y'all have some work in progress in any state, please share by Wednesday -- my bigger aim is to improve string literal docs in general, so it'll conflict :)

[davepeck]

More TODOs added

[davepeck]

Documentation is starting to collect at https://github.com/t-strings/cpython/tree/docs/pep750-templatelib