`getDescendantAtStartWithWidth` does not work for reported diagnostic on exported functions

**Describe the bug**
See the repro

Version: 20.0.0

**To Reproduce**

```ts
import { Project } from "ts-morph";

const project = new Project();

const inputCode = `namespace test {
export function addTwoNumbers(first: number, second: number) {
return first + second;
}

export function testBug() {
return test.addTwoNumbers(1);
}
}
`;

project.createSourceFile("main.ts", inputCode);

const diagnostics = project.getPreEmitDiagnostics();

for (const d of diagnostics) {
const sourceFile = d.getSourceFile()!;

const start = d.getStart();
const length = d.getLength();

if (start && length) {
// This is undefined
const errorNode = sourceFile.getDescendantAtStartWithWidth(start, length);
console.log(`Error node text: ${errorNode.getText()}`);
}
}

```

**Expected behavior**
`errorNode` should not be undefined

**Actual behavior**
`errorNode` is undefined
If you remove `export` from `addTwoNumbers`, it works

**Known workaround:**
Use `const errorNode = sourceFile.getDescendantAtPos(start);`

Run the TypeScript reproduction from the issue and inspect the diagnostic returned by Project.getPreEmitDiagnostics(). Start at sourceFile.getDescendantAtStartWithWidth and compare it with sourceFile.getDescendantAtPos, using the exported and non-exported function cases. Done means the reported diagnostic resolves to a node instead of undefined for the exported-function case.

Written by the indexing model from the issue text.