Fix bug Muter visitor transform using wrong syntax

[hoangatuan]

Problems
Passing the wrong Syntax, which leads to crashes when running muter.

Fix
We should pass the original Syntax into the length paramater

[ZevEisenberg]

Thanks! Any chance you could provide a project that reproduces and/or a unit test?

[hoangatuan]

@ZevEisenberg

Given this code:

extension ClassA {

    // Verify that the input is legal
    @discardableResult
    func isInputNumberValid() -> Bool {

        let message = type == .caseA
            ? "caseAString"
            : "defaultStirng"

        return false
    }
}

When run muter:

[hoangatuan]

The reason is that when running muter, we also format the _mutate project. That's why the node.description.utf8.count and mutatedSyntax.description.utf8.count is different

[hoangatuan]

Also based on the Apple document, the length field should be the length of the original code. So we're passing the wrong value here