Fix text decoration color fallback to use per-span foreground color

Summary:
D104680895 replaced `ReactUnderlineSpan`/`ReactStrikethroughSpan` with custom `CanvasEffectSpan` drawing, but when `textDecorationColor` is not explicitly set, it fell back to `layout.paint.color` (the base paint color, typically black) instead of the text's actual foreground color. This caused decorations to render in the wrong color for text with `ForegroundColorSpan` — e.g., white text on dark backgrounds got black underlines, teal link text got black underlines.

This diff fixes the color by looking up the `ForegroundColorSpan` at the decoration's character position and using its color as the fallback instead of the base paint color.

Changelog: [Android][Fixed] - Fix text decoration color not matching foreground color when `textDecorationColor` is not set

Reviewed By: javache

Differential Revision: D107645191

fbshipit-source-id: b1e0a616259c983ae57cdbf476ae97da4204d906

Author: cortinico

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/text/TextDecorationStyle.kt

@@ -14,6 +14,8 @@ import android.graphics.Paint
 import android.graphics.Path
 import android.os.Build
 import android.text.Layout
+import android.text.Spanned
+import android.text.style.ForegroundColorSpan
 import kotlin.math.max
 import kotlin.math.min
 import kotlin.math.roundToInt
@@ -126,7 +128,18 @@ internal fun drawSpannedDecoration(
     yOffsetForLine: (paint: Paint, baseline: Float, thickness: Float) -> Float,
 ) {
   val textPaint = layout.paint
-  val effectiveColor = if (color != Color.TRANSPARENT) color else textPaint.color
+  val effectiveColor =
+      if (color != Color.TRANSPARENT) {
+        color
+      } else {
+        // Look up the actual foreground color at the span position. layout.paint
+        // is the base paint whose color may differ from per-span foreground colors
+        // applied via ForegroundColorSpan (e.g., link text, colored text).
+        val spanned = layout.text as? Spanned
+        val fgSpans = spanned?.getSpans(start, start + 1, ForegroundColorSpan::class.java)
+        if (fgSpans != null && fgSpans.isNotEmpty()) fgSpans.last().foregroundColor
+        else textPaint.color
+      }
   val minThickness = 1.5f * textPaint.density
   val thickness =
       if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {