Add KDoc documentation to BlendModeHelper (#54347)

Summary:
Pull Request resolved: #54347

Added comprehensive KDoc documentation to the BlendModeHelper object and its public method for parsing CSS mix-blend-mode properties on Android Q+.

changelog: [internal] internal

Reviewed By: lenaic

Differential Revision: D85926891

fbshipit-source-id: bcafa6b02281d5265f59b34641847bc3b19d6604

Author: mdvacca

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/BlendModeHelper.kt

@@ -14,10 +14,23 @@ import android.view.ViewGroup
 import androidx.core.view.children
 import com.facebook.react.R
 
+/**
+ * Helper object for parsing and handling CSS mix-blend-mode properties on Android Q+ (API 29+).
+ *
+ * This object provides utilities to convert CSS mix-blend-mode string values into Android's
+ * [BlendMode] enumeration and to determine when views need isolated layers for proper blending.
+ */
 @TargetApi(29)
 internal object BlendModeHelper {
 
-  /** @see <a href="https://www.w3.org/TR/compositing-1/#mix-blend-mode">mix-blend-mode</a> */
+  /**
+   * Parses a CSS mix-blend-mode string value into an Android BlendMode.
+   *
+   * @param mixBlendMode The CSS mix-blend-mode value (e.g., "multiply", "screen", "overlay")
+   * @return The corresponding [BlendMode], or null if "normal" or on unsupported Android versions
+   * @throws IllegalArgumentException if the mix-blend-mode name is invalid
+   * @see <a href="https://www.w3.org/TR/compositing-1/#mix-blend-mode">mix-blend-mode</a>
+   */
   @JvmStatic
   fun parseMixBlendMode(mixBlendMode: String?): BlendMode? {
     if (mixBlendMode == null || Build.VERSION.SDK_INT < Build.VERSION_CODES.Q) {