give a better example why std modules named like primitives are needed

[cyrgani]

A small update to the std lib.rs introduction to replace mentions of std::i32 (never needed) with std::char (sometimes needed).
Related to #146882.

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[xizheyin]

Would it be better to use “rarely used” to make the expression more neutral?
In module char doc, it presents there are some useful items:

This module is the home of the iterator implementations for the iterators implemented on char, as well as some useful constants and conversion functions that convert various types to char.

And would this be a better way to express it?

//! `char`](primitive::char) that lists all the methods that can be called on
//! characters (very useful), and there is a [page for the module
//! `std::char`] that documents utility types, constants, and conversion functions
//! (rarely used).

[cyrgani]

I would prefer not mentioning the constants and conversion functions here, since they all already exist on the primitive type char itself and do not need to be used anymore, just as it is with std::i32::{MIN, MAX};.

[ibraheemdev]

Thanks. @bors r+ rollup

[bors]

📌 Commit 0bc6945 has been approved by ibraheemdev

It is now in the queue for this repository.