Drop 'strong discouragement' of nested block-local variables

[leiflindholm]

The rules explicitly permit variable definitions such as
if (Condition) {
UINTN Example;
...
}

But for some reason it simultaneously "strongly discourages" from it. This feels entirely wrong to me; the codebase suffers from too-long functions with too many live variables making compilers' work more difficult - preventing optimisations and periodically throwing up warnings/errors as compilers change.

Change the strong discouragement to a note on not confusing variable scope.

[mdkinney]

I think there would a couple reasons for this restriction. The change needs to describe what has changed since the rules were established to justify the change.

• Avoid use of same named local variable at different scopes within a function that can make code review and maintenance challenging
• Be able to review stack usage from local variables by reviewing declarations in one location at beginning of a function instead of searching for additional declarations throughout the function. For env where the stack size is very limited, it is important to not use large structs or arrays as local variables.

[mdkinney]

@ajfish Please provide background for original rules for local variable declarations.

[makubacki]

Pending any empirical concerns, I favor this change and the file content update.