Improve CA1802 Documentation with Warnings About Potential Risks of Using const

[shethaadit]

Summary

This update enhances the documentation for CA1802 by:

• Adding a warning about the risks of replacing static readonly with const for public and externally visible members.
• Clarifying that const is safe for private members and generally safe for internal members unless exposed via InternalsVisibleTo or deployed separately.

Fixes #40827

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Internal previews

📄 File	🔗 Preview link
docs/fundamentals/code-analysis/quality-rules/ca1802.md	CA1802: Use Literals Where Appropriate

[gewarren]

Thanks @shethaadit. @BillWagner could you review from a C# perspective?

[gewarren]

Suggested change

	> For public or externally visible members, changing `static readonly` to `const` can lead to issues. `const` values are embedded in dependent assemblies at compile time, so changes in the library's value may not propagate, potentially causing errors. Suppress this rule if the value might change in the future.
	> For public or externally visible members, changing `static readonly` to `const` can lead to issues. `const` values are embedded in dependent assemblies at compile time, so changes in the library's value might not propagate, potentially causing errors. If the value of your member might change in the future, suppress this rule.