Fix text truncation caused by pixel-grid rounding of near-integer text nodes

[stleamist]

Summary

Fixes a text truncation bug in roundLayoutResultsToPixelGrid(): when a text node's scaled dimension is close to a whole number (hasFractionalWidth == false), the trailing edge was force-floored. Because the inexactEquals tolerance (0.0001) can apply asymmetrically to the two edges of the same node, the leading edge may snap up while the trailing edge gets floored, producing a final width smaller than the measured text width — so the text renders with an ellipsis.

Real-world case

Observed with a right-aligned UILabel laid out via FlexLayout on an @3x display (393pt-wide device). The measured text width was 54.666656, positioned at absoluteNodeLeft = 163.666641:

Value	× 3 (scale)	distance from whole number	within 0.0001 tolerance?	result
nodeWidth = 54.666656	163.999968	0.000032	yes → hasFractionalWidth = false	forceFloor enabled
absoluteNodeLeft = 163.666641	490.999923	0.000077	yes	snaps up to 491
absoluteNodeRight = 218.333297	654.999891	0.000109	no	floored down to 654

Final width = (654 − 491) / 3 = 54.333… < measured 54.666656 → truncated.

Both edges sit essentially on the same pixel boundary, but a 0.00003 difference makes them round in opposite directions, shrinking the node by a full pixel.

Fix

Never force-floor the trailing edge of a text node:

• hasFractionalWidth == true (clearly fractional): keep the existing force-ceil behavior.
• hasFractionalWidth == false (near-integer): fall through to natural rounding, which snaps 654.999891 up to 655 and preserves the measured width.

This also matches the intent of the existing comment in the function: "If a node has a custom measure function we never want to round down its size as this could lead to unwanted text truncation."

Tests

• All existing tests pass unchanged (831 passed, 46 skipped, 0 failed).
• Adds tests/YGRoundingTextTruncationTest.cpp with four tests, including one reproducing the exact values from the real-world case above (fails before the fix, passes after).

Related issues

• Fix layout bug caused by floating point rounding error #1860 addresses the same class of bug for height only and notes that "a similar change for width may be helpful" — this PR covers both width and height at the rounding call sites.
• Likely also addresses Layout bug caused by floating point rounding error #749 and Why can't we round node width/height directly in roundLayoutResultsToPixelGrid()? #1574, which report measured text being rounded down by the pixel grid.

[stleamist]

I've put together a minimal iOS reproduction of this bug that uses nothing but the yoga C API and a single UILabel, with snapshot tests: https://github.com/stleamist/YogaTruncationRepro

The label is measured by a yoga measure function and laid out on a @3x pixel grid (iPhone 15 Pro simulator) at an offset where the node's left edge scales to just inside the 0.0001 inexactEquals tolerance of a whole pixel (so it snaps up) while the right edge lands just outside it (so it gets force-floored). Yoga assigns the label exactly one pixel less than what its measure function returned, and the label renders with an ellipsis:

XCTAssertGreaterThanOrEqual failed: ("45.0") is less than ("45.33332266666667")

yoga main (f6206ec3)	with this PR

The core of the trigger (full code in the repo):

// Measure the real label, then nudge the width up to the next value whose
// scaled size sits just inside the tolerance of a whole pixel — the same
// shape of value that real text measurement produces naturally. This makes
// hasFractionalWidth == false, enabling the force-floor path.
CGSize fitted = [view.label sizeThatFits:CGSizeMake(CGFLOAT_MAX, CGFLOAT_MAX)];
double wholePixels = ceil(fitted.width * 3.0);
double measuredWidth = (wholePixels - 0.000032) / 3.0;

// Left edge: scales to 490.999923, *within* 0.0001 of 491 → snaps UP.
// Right edge (left + width): ends up ~0.000109 away from a whole pixel,
// *outside* the tolerance → force-floored DOWN. The node loses one pixel.
YGNodeStyleSetPadding(root, YGEdgeLeft, (float)((491.0 - 0.000077) / 3.0));

The package pins yoga to current main (f6206ec3), so both tests fail out of the box. Swapping the dependency for this PR's branch (a one-line change noted in Package.swift) makes both pass. The snapshot test's committed reference is the correct rendering, so its failure diff visualizes the truncation directly.