While #16444 left wavy lines in an amazing state already, there were
a few more things that could be done to make GDI look more consistent
with other well known Windows applications.

But before that, a couple unrelated, but helpful changes were made:
* `GdiEngine::UpdateFont` was heavily modified to do all calculations
  in floats. All modern CPUs have fast FPUs and even the fairly slow
  `lroundf` function is so fast (relatively) nowadays that in a cold
  path like this, we can liberally call it to convert back to `int`s.
  This makes intermediate calculation more accurate and consistent.
* `GdiEngine::PaintBufferGridLines` was exception-unsafe due to its
  use of a `std::vector` with catch clause and this PR fixes that.
  Additionally, the vector was swapped out with a `til::small_vector`
  to reduce heap allocations. (Arena allocators!)
* RenderingTests was updated to cover styled underlines

With that in place, these improvements were done:
* Word's double-underline algorithm was ported over from `AtlasEngine`.
  It uses a half underline-width (aka `thinLineWidth`) which will now
  also be used for wavy lines to make them look a bit more filigrane.
* The Bézier curve for wavy/curly underlines was modified to use
  control points at (0.5,0.5) and (0.5,-0.5) respectively. This results
  in a maxima at y=0.1414 which is much closer to a sine curve with a
  maxima at 1/(2pi) = 0.1592. Previously, the maxima was a lot higher
  (roughly 4x) depending on the aspect ratio of the glyphs.
* Wavy underlines don't depend on the aspect ratio of glyphs anymore.
  This previously led to several problems depending on the exact font.
  The old renderer would draw exactly 3 periods of the wave into
  each cell which would also ensure continuity between cells.
  Unfortunately, this meant that waves could look inconsistent.
  The new approach always uses the aforementioned sine-like waves.
* The wavy underline offset was clamped so that it's never outside of
  bounds of a line. This avoids clipping.

* Compile RenderingTests and run it
* Using Consolas, MS Gothic and Cascadia Code while Ctrl+Scrolling
  up and down works as expected without clipping ✅

(cherry picked from commit 99193c9)
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