UFPWriter: fix serialization of SettingFunctions

[Piezoid]

PR #13209 adds the modified settings to the UFP exports. The settings are serialized as JSON but doesn't handles the SettingFunctions. This was also reported by users in emtrax-ltd/Cura2MoonrakerPlugin#55.

Reproduction steps:: Modify a setting with a computed default, then click the icon. Slice and save the result as a .ufp file. Cura will crash with:

Traceback (most recent call last):
  File "Cura/cura/CuraApplication.py", line 1127, in event
    return super().event(event)
  File "Uranium/UM/Qt/QtApplication.py", line 502, in event
    event._function_event.call()
  File "Uranium/UM/Event.py", line 218, in call
    self._function(*self._args, **self._kwargs)
  File "Cura/cura/Utils/Threading.py", line 34, in _handle_call
    ico.result = func(*args, **kwargs)
  File "Cura/plugins/UFPWriter/UFPWriter.py", line 87, in write
    json.dump(self._getSliceMetadata(), setting_textio, separators=(", ", ": "), indent=4)
  File "$HOME/.conan/data/cpython/3.10.4/_/_/package/9054a82b60899c3ed90865d5b990fd99ef2dc167/lib/python3.10/json/__init__.py", line 179, in dump
    for chunk in iterable:
  File "$HOME/.conan/data/cpython/3.10.4/_/_/package/9054a82b60899c3ed90865d5b990fd99ef2dc167/lib/python3.10/json/encoder.py", line 431, in _iterencode
    yield from _iterencode_dict(o, _current_indent_level)
  File "$HOME/.conan/data/cpython/3.10.4/_/_/package/9054a82b60899c3ed90865d5b990fd99ef2dc167/lib/python3.10/json/encoder.py", line 405, in _iterencode_dict
    yield from chunks
  File "$HOME/.conan/data/cpython/3.10.4/_/_/package/9054a82b60899c3ed90865d5b990fd99ef2dc167/lib/python3.10/json/encoder.py", line 405, in _iterencode_dict
    yield from chunks
  File "$HOME/.conan/data/cpython/3.10.4/_/_/package/9054a82b60899c3ed90865d5b990fd99ef2dc167/lib/python3.10/json/encoder.py", line 405, in _iterencode_dict
    yield from chunks
  File "$HOME/.conan/data/cpython/3.10.4/_/_/package/9054a82b60899c3ed90865d5b990fd99ef2dc167/lib/python3.10/json/encoder.py", line 438, in _iterencode
    o = _default(o)
  File "$HOME/.conan/data/cpython/3.10.4/_/_/package/9054a82b60899c3ed90865d5b990fd99ef2dc167/lib/python3.10/json/encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type SettingFunction is not JSON serializable

This patch mimics what GcodeWriter does, calling str() on the setting values.

[jellespijker]

@Piezoid good catch can ypu merge this against the 5.2 branch though

[jellespijker]

@Joeydelarago can you do the review and component test and create a jira ticket for this since you qorked on that feature

[nallath]

Hmm, this isn't quite correct! In this case the values need to be "flattened" so that you get key value pairs (without any setting functions in it).

if isinstance(property_value, SettingFunction):
    property_value = property_value(global_stack)

[Piezoid]

Hmm, this isn't quite correct! In this case the values need to be "flattened" so that you get key value pairs (without any setting functions in it).

Yes, I don't know anything about the receiving end for this metadata, that is why I asked if this solution was ok. I went for the simplest solution since I wasn't aware that SettingFunction could be evaluated that way.

[Piezoid]

@nallath BTW, I think that the action should clear the setting override if the default setting value is that same function. Currently a setting reset with this button will be shown in the changes list.

[nallath]

Yeah, no worries. We will change it. We should have done this from the start, but we missed it...