[llvm] [CodingStandard] Rework anonymous namespace section to cover visibility more broadly (PR #126775)

[Aaron Ballman via llvm-commits]

================
@@ -1579,17 +1579,23 @@ clarification.
 
 .. _static:
 
-Anonymous Namespaces
-^^^^^^^^^^^^^^^^^^^^
-
-After talking about namespaces in general, you may be wondering about anonymous
-namespaces in particular.  Anonymous namespaces are a great language feature
-that tells the C++ compiler that the contents of the namespace are only visible
-within the current translation unit, allowing more aggressive optimization and
-eliminating the possibility of symbol name collisions.  Anonymous namespaces are
-to C++ as "static" is to C functions and global variables.  While "``static``"
-is available in C++, anonymous namespaces are more general: they can make entire
-classes private to a file.
+Restrict Visibility
+^^^^^^^^^^^^^^^^^^^
+
+Functions and variables should have the most restricted visibility possible.
+For class members, that means using appropriate `private`, `protected` or `public`
+keyword to restrict their access. For non-member functions, variables and classes,
----------------
AaronBallman wrote:

```suggestion
For class members, that means using appropriate `private`, `protected`, or `public`
keyword to restrict their access. For non-member functions, variables, and classes,
```

https://github.com/llvm/llvm-project/pull/126775