Update patterns.md with empty property pattern details

[AdmiralSnyder]

Clarify the behavior of the empty property pattern in C#.

Summary

added note about the empty property pattern because it wasn't mentioned anywhere.

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Internal previews

📄 File	🔗 Preview link
docs/csharp/language-reference/operators/patterns.md	Pattern matching - the is and switch expressions, and operators and, or, and not in patterns

[Copilot]

Pull Request Overview

This PR adds clarification about the behavior of the empty property pattern (is { }) in C#, which was previously undocumented in the patterns documentation.

Key Changes:

• Added a note explaining that the empty property pattern is { } matches all non-null values and can be used as an alternative to is not null for creating variables.

[Copilot]

Corrected spelling of 'specifially' to 'specifically'.

Suggested change

	This specifially means that the *empty* property pattern `is { }` matches everything non-null, and can be used instead of the `is not null` to create a variable: `somethingPossiblyNull is { } somethingDefinitelyNotNull`.
	This specifically means that the *empty* property pattern `is { }` matches everything non-null, and can be used instead of the `is not null` to create a variable: `somethingPossiblyNull is { } somethingDefinitelyNotNull`.

[BillWagner]

Hi @AdmiralSnyder

I like this change. I think it would be more clear to readers if you added an example of is { } as a null check. Can you make that addition?

[AdmiralSnyder]

hi @BillWagner i didn't know how the
:::code language="csharp" source="snippets/patterns/PropertyPattern.cs" id="WithTypeCheck":::
worked, or rather, how i add a second file into the commit/PR from the github UI (using the convenient "edit" function) - you mean, that, right?

or do you mean just expanding the inline code ?

[BillWagner]

@AdmiralSnyder

Adding a second file in the same PR isn't easy in the GitHub UI. If you add an inline example, I'll move it to the included snippets.