Fix bug in unusedArguments when shadowing function argument with conditional assignment declaration

[calda]

This PR fixes a bug in the unusedArguments rule when shadowing a function argument with a declaration where the value is an if or switch expression.

Before (argument unexpectedly marked as unused)

func test(foo _: Foo) {
    let foo =
        if foo.bar {
            baaz
        } else {
            bar
        }
    print(foo)
}

After (preserved)

func test(foo: Foo) {
    let foo =
        if foo.bar {
            baaz
        } else {
            bar
        }
    print(foo)
}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.20%. Comparing base (3ed1b63) to head (fbd398e).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1687   +/-   ##
========================================
  Coverage    95.19%   95.20%           
========================================
  Files           21       21           
  Lines        23019    23023    +4     
========================================
+ Hits         21913    21918    +5     
+ Misses        1106     1105    -1     

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