Add resolution guidance to CS1023 compiler error documentation

[Copilot]

The CS1023 compiler error documentation was missing resolution guidance, leaving developers without clear instructions on how to fix the error. This enhancement adds:

What was added:

• Clear resolution section explaining that braces are needed to create block statements
• Complete corrected code examples showing the proper solution
• Brief explanation of why C# requires this (scope rules) and how it differs from C/C++

Before: The documentation only showed what causes the error but not how to fix it.

After: Developers now have practical examples showing both the problematic code and the corrected version:

// Problem - generates CS1023
if (condition)
    int i;  // CS1023: declaration not valid here

// Solution - wrap in braces
if (condition)
{
    int i;  // Fixed: now in a block statement
}

The changes follow the established pattern used in other CS error documentation (like CS0017 and CS0131) that include "To resolve this error" sections with practical solutions.

Fixes #28064.

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Internal previews

📄 File	🔗 Preview link
docs/csharp/misc/cs1023.md	docs/csharp/misc/cs1023

[BillWagner]

This also LGTM. It's ready for final review