fix: preserve MXCSR around earcut triangulation to support UE5 builds…

[Johnly1986]

… UE5 enables SSE DAZ (Denormals Are Zero) and FTZ (Flush To Zero) MXCSR flags on worker threads in packaged Development/Shipping builds. These flags cause mapbox::earcut's floating-point geometry predicates (signed area, point-in-triangle, etc.) to flush denormal intermediate values to zero, producing incorrect triangulation results for polygons with near-collinear vertices.

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[azrogers]

@Johnly1986 Thanks for the PR! Can you run down the author checklist in the template there? Particularly we need you to fill out the Contributor License Agreement - otherwise we can't take a look at your code!