[TASK] Converting InputData ParameterInput back to XML

Issue Description

Is your feature request related to a problem? Please describe. In RAVEN and HERON, input specs are created using ParameterInput classes within ravenframework.utils.InputData. These have the capability of being populated with data from XML files (data which is loaded and stored in ElementTree format then converted to ParameterInput classes). It would be useful if there was a way to convert the data from ParameterInput back to ElementTree XML format.

Describe the solution you'd like Within the ParameterInput class, there could be a method to recursively look through the attributes, values and subnodes of the given ParameterInput object; if there are subnodes which are also ParameterInput objects, we would loop through those as well.

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

For Change Control Board: Issue Review

This review should occur before any development is performed as a response to this issue.

[x] 1. Is it tagged with a type: defect or task?
[x] 2. Is it tagged with a priority: critical, normal or minor?
[x] 3. If it will impact requirements or requirements tests, is it tagged with requirements?
[x] 4. If it is a defect, can it cause wrong results for users? If so an email needs to be sent to the users.
[x] 5. Is a rationale provided? (Such as explaining why the improvement is needed or why current code is wrong.)

For Change Control Board: Issue Closure

This review should occur when the issue is imminently going to be closed.

[x] 1. If the issue is a defect, is the defect fixed?
[x] 2. If the issue is a defect, is the defect tested for in the regression test system? (If not explain why not.)
[x] 3. If the issue can impact users, has an email to the users group been written (the email should specify if the defect impacts stable or master)?
[x] 4. If the issue is a defect, does it impact the latest release branch? If yes, is there any issue tagged with release (create if needed)?
[x] 5. If the issue is being closed without a pull request, has an explanation of why it is being closed been provided?

idaholab / raven