Ruby: support sprintf formatted string with modulo operator

I noticed that dataflow in Ruby isn't propagated to [Kernel.sprintf](https://ruby-doc.org/3.2.2/String.html#method-i-25) formatted strings, e.g. the stored xss query should flag this code in an ERB template:

```rb
<%# BAD: Kernel.sprintf modulo operator syntax %>
<%= "Welcome %{user}".html_safe % { user: @user.handle } %>
```

The string literal is parsed as a a single `Ast::StringTextComponent`, where it should probably also contain a `Ast::StringInterpolationComponent`. I tried to work around this problem using an additional taint step:

```ql
predicate isAdditionalSprintfTaintStep(DataFlow::Node node1, DataFlow::Node node2) {
exists(ModuloExpr expr, HashLiteral hash, StringLiteral str |
hash.getParent*() = expr.getRightOperand() and
str.getParent*() = expr.getLeftOperand() and
hash.getAKeyValuePair().getValue() = node1.asExpr().getExpr() and
str = node2.asExpr().getExpr()
)
}
```

which works for the code snippet above, but doesn't work when the dataflow gets a bit more complex:

```rb
<% sink = "Welcome %{user}".html_safe %>
<%= sink % { user: @user.handle } %>
```

I tried the following, but it doesn't work:

```ql
predicate isAdditionalSprintfTaintStep(DataFlow::Node node1, DataFlow::Node node2) {
exists(ModuloExpr expr, HashLiteral hash, StringLiteral str |
DataFlow::localExprFlow(hash.getAControlFlowNode(), expr.getRightOperand().getAControlFlowNode()) and
DataFlow::localExprFlow(str.getAControlFlowNode(), expr.getLeftOperand().getAControlFlowNode()) and
hash.getAKeyValuePair().getValue() = node1.asExpr().getExpr() and
str = node2.asExpr().getExpr()
)
}
```

How do I catch the insecure code snippet above using local dataflow?

Start with the Ruby handling of Kernel.sprintf modulo syntax and the Ast::StringTextComponent versus Ast::StringInterpolationComponent behavior described in the issue. Compare the two ERB examples with the attempted isAdditionalSprintfTaintStep predicates and local dataflow calls; done means the stored-XSS example is caught through local dataflow, including when the formatted string is assigned to sink first.

Vom Indexierungsmodell aus dem Issue-Text verfasst.