BeginDrawing: INTENDED_VSYNC_TIMESTAMP -> VSYNC_TIMESTAMP (#54765)

Summary:
Pull Request resolved: #54765

# Changelog: [Internal]

Looking at the Chrome DevTools Frontend code, the `BeginFrame` trace event represents the actual start of the frame sequence, not the expected one.

Using inteded timestamp doesn't seem right here:
 - [INTENDED_VSYNC_TIMESTAMP](https://developer.android.com/reference/android/view/FrameMetrics#INTENDED_VSYNC_TIMESTAMP)
 - [VSYNC_TIMESTAMP](https://developer.android.com/reference/android/view/FrameMetrics#VSYNC_TIMESTAMP)

INTENDED_VSYNC_TIMESTAMP description says:
> The intended start point for the frame. If this value is different from VSYNC_TIMESTAMP, there was work occurring on the UI thread that prevented it from responding to the vsync signal in a timely fashion.

Reviewed By: sbuggay

Differential Revision: D88088882

fbshipit-source-id: 0980c4952b7b71dd8ea2333334f0ed89f6ecedb1

Author: hoxyq

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/devsupport/inspector/FrameTimingsObserver.kt

@@ -36,7 +36,7 @@ internal class FrameTimingsObserver(
 
   private val frameMetricsListener =
       Window.OnFrameMetricsAvailableListener { _, frameMetrics, _dropCount ->
-        val beginDrawingTimestamp = frameMetrics.getMetric(FrameMetrics.INTENDED_VSYNC_TIMESTAMP)
+        val beginDrawingTimestamp = frameMetrics.getMetric(FrameMetrics.VSYNC_TIMESTAMP)
         val commitTimestamp =
             beginDrawingTimestamp + frameMetrics.getMetric(FrameMetrics.INPUT_HANDLING_DURATION)
         +frameMetrics.getMetric(FrameMetrics.ANIMATION_DURATION)