Implement From<T> for types that implements From<&T> and Into<T>, and vice versa

[jnbooth]

There's an odd pattern across many files that looks like this:

impl From<&QLine> for QLineF {
    fn from(line: &QLine) -> Self {
        ffi::qlinef_from_qline(line)
    }
}

impl From<QLineF> for QLine {
    fn from(value: QLineF) -> Self {
        value.to_line()
    }
}

One of the implementations uses a borrow, and the other one does not, even though both are calling functions that take references. Theoretically, in order to be consistent with Qt, both implementations should use borrowing (From<&QLine> and From<&QLineF>). But I don't think it would make sense to remove the by-value implementations, because A) that would be a breaking change, and B) it is useful to be able to do e.g. let pointf = QPoint::new(1, 2).into() rather than let pointf = (&QPoint::new(1, 2)).into(). So instead, I just added complementary implementations so now From<QLine> for QLineF and From<&QLineF> for QLine are implemented as well.

That said, I'm not sure why QPen implements From<&PenStyle>. I added an implementation for From<PenStyle>, so that part is handled, but at some point it might be worth removing the From<&PenStyle> implementation, because PenStyle is just an i32 enum. There's no point in passing it by reference rather than value.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (c98fb62) to head (35a6192).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1384   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           75        75           
  Lines        13108     13108           
=========================================
  Hits         13108     13108           

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