Update length/capacity exceptions for .NET 11

[gewarren]

Contributes to dotnet/docs#49545.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-io

[Copilot]

Pull request overview

This PR updates the MemoryStream documentation to reflect .NET 11 changes regarding length and capacity exceptions. The primary focus is documenting the new maximum value (0x7FFFFFC7 bytes) for capacity and length operations introduced in .NET 11.

Key changes include:

• Adding .NET 11-specific exception documentation for Capacity property and SetLength method
• Fixing xref formatting by removing .%2A suffixes from property references
• Improving documentation formatting and consistency

[BillWagner]

This LGTM @gewarren

Let's