False positive: it is valid to escape $ in javascript template string syntax

**Description of the false positive**

js/useless-regexp-character-escape triggers for code like:

```javascript
const str = `hello \${name}`;
```

This is invalid, since without the backslash escape, that's a string interpolation of the `name` variable:

```javascript
const str = `hello ${name}`;
```

This triggered in the lit-html codebase on this line: https://github.com/lit/lit/blob/5eea178e0df1199cd29e9d46bc888d52882f18dd/packages/lit-html/src/lit-html.ts#L1418

Link to the code scanning issue: https://github.com/lit/lit/security/code-scanning/15

Start by locating the js/useless-regexp-character-escape query and review how it handles JavaScript template strings. Use the escaped interpolation example from the issue as the reproduction case, then verify that it is no longer reported while the unescaped ${name} form remains correctly distinguished.

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