OOXMLValidator: issues with ordering of strong vs emph

[edwintorok]

Explain the problem.
This seems to be now the only remaining validation error:

which dotnet || ("dotnet is required" && exit 1)
/usr/bin/dotnet
which json_reformat || ("json_reformat is required" && exit 1)
/usr/bin/json_reformat
test -d ./OOXML-Validator || \
        (git clone https://github.com/mikeebowen/OOXML-Validator.git \
        && cd OOXML-Validator && dotnet build --configuration=Release)
dotnet run --no-build --no-restore --project OOXML-Validator/OOXMLValidatorCLI -- test/docx/golden -r | json_reformat

[
    {
        "FilePath": "test/docx/golden/inline_formatting.docx",
        "ValidationErrors": "[{\"Description\":\"The element has unexpected child element 'http://schemas.openxmlformats.org/wordprocessingml/2006/main:b'.\",\"Path\":{\"NamespacesDefinitions\":[\"xmlns:w=\\\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\\\"\"],\"Namespaces\":{},\"XPath\":\"/w:document[1]/w:body[1]/w:p[1]/w:r[7]/w:rPr[1]\",\"PartUri\":\"/word/document.xml\"},\"Id\":\"Sch_UnexpectedElementContentExpectingComplex\",\"ErrorType\":\"Schema\"}]"
    }
]

As the comment in the code explains though (Combine.hs) the order can be either Strong(Emph(..)), or Emph(Strong(..)),
so this might need to be sorted when flattened.

Pandoc version?
Latest main + my PR

[edwintorok]

BTW this is really minor, everything else seems to be fine now wrt to validation after the linked PR.