bpo-46113: Minor fixes in stdtypes documentation (GH-30167) (GH-30186)

* Fix-1 - isidentifier() function output

* Fix-2 Update the str.splitlines() function parameter

* Fix-3 Removed unwanted full stop for str and bytes types double quotes examples.

* Fix-4 Updated class dict from **kwarg to **kwargs
(cherry picked from commit 6f2df4295123f8b961d49474b7668f7564a534a4)

Co-authored-by: Vivek Vashist <vivekvashist@gmail.com>