Fix handling of Puppet::Pops serialization issues

[seanmil]

Short description

In Puppet::Pops::Serialization::ToDataConverter a number of different issues can occur during serialization. If an issue is generated and the PuppetStack is not at the top of stack it attempts to include file/line position information but the method call to stacktrace isn't in scope at the call, causing a fatal error. Calling Puppet::Pops::PuppetStack.stacktrace obtains the desired stacktrace for position information.

Checklist

I have:

• read the CONTRIBUTING.md document
• read and accepted the Developer Certificate of Origin document and added a Signed-off-by annotation to each of my commits
• read and accepted the AI Policy document and added Generated-by or Assisted-by annotations to each of my commits created with the help of an AI agent
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)