gh-74929: PEP 667 general docs update (gh-119201)

* expand on What's New entry for PEP 667 (including porting notes)
* define 'optimized scope' as a glossary term
* cover comprehensions and generator expressions in locals() docs
* review all mentions of "locals" in documentation (updating if needed)
* review all mentions of "f_locals" in documentation (updating if needed)

Lib/code.py

@@ -25,10 +25,10 @@ class InteractiveInterpreter:
     def __init__(self, locals=None):
         """Constructor.
 
-        The optional 'locals' argument specifies the dictionary in
-        which code will be executed; it defaults to a newly created
-        dictionary with key "__name__" set to "__console__" and key
-        "__doc__" set to None.
+        The optional 'locals' argument specifies a mapping to use as the
+        namespace in which code will be executed; it defaults to a newly
+        created dictionary with key "__name__" set to "__console__" and
+        key "__doc__" set to None.
 
         """
         if locals is None: