support let-else statement for CFG

[White-Green]

fix: #9681 (cc: @ortem)
Follow-up for #7798

This pull request addresses issue #9681 by correctly handling the else block of let-else statements in the construction of the ControlFlowGraph.

Due to issues with my environment, not all tests could be executed. I apologize if any failures occurred.

changelog: Fix false-positive detection of unreachable code with let else syntax

[artemmukhin]

@White-Green Thank you, and welcome to IntelliJ Rust! As a first-time contributor, you can add your username to CONTRIBUTORS.txt file.

Could you please clarify what kind of issue you have with tests? Maybe we can help. Also, CONTRIBUTING.md file might help to learn more about the project setup.

[artemmukhin]

Please handle let-else syntax in org.rust.lang.core.dfa.ExprUseWalker#walkLet and add the corresponding test cases to RsUnreachableCodeInspectionTest

[Undin]

As a first-time contributor, you can add your username to CONTRIBUTORS.txt file.

Note, we don't collect contributors' usernames anymore since we don't need to check CLA

[White-Green]

@ortem Thank you for pointing out the missing.
I fixed it.

[artemmukhin]

LGTM, just one minor comment.
Before we merge it, please squash your commits into one and force-push it

[artemmukhin]

@White-Green Thank you again, and welcome to IntelliJ Rust contributors!

bors r+

[bors]

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