XmlContext allows for more than one text node per model

[tefra]

The XmlContent expects dataclasses fields metadata to include the xml type parameter with one of Element | Attribute | Wildcard | Attributes otherwise defaults to Text.

There are currently no sanity checks like multiple text nodes in the same model.
The builder should detect these cases and revert to all Elements.

@dataclass
class Example:
    bool: bool
    int: int
    union: Union[int, bool]

result = list(self.ctx.get_type_hints(Example, None))
expected = [
    XmlText(name="bool", qname="bool", types=[bool]),
    XmlText(name="int", qname="int", types=[int]),
    XmlText(name="union", qname="union", types=[bool, int]),
]

Which of course is impossible, the correct output should be

expected = [
    XmlElement(name="bool", qname="bool", types=[bool]),
    XmlElement(name="int", qname="int", types=[int]),
    XmlElement(name="union", qname="union", types=[bool, int]),
]

Another example should be

@dataclass
class Example:
    bool: bool
    int: int
    union: Union[int, bool]
    text: str = field(metadata=dict(type="Text"))


result = list(self.ctx.get_type_hints(Example, None))
expected = [
    XmlText(name="bool", qname="bool", types=[bool]),
    XmlText(name="int", qname="int", types=[int]),
    XmlText(name="union", qname="union", types=[bool, int]),
]

This will also make writing the models manually a little easier and might also allow the generator to cut down on declarations a little bit.