Update the RTCRtpReceiver Decoder State Changed and Error Events explainer (#1354)

This change
- Simplifies the existing `decoderstatechange` event (drops
`codecString` and
`powerEfficient`). The codec can be read from the receiver's
`getStats()`.
 - Adds a new `decodererror` event that surfaces a `DOMException`.

Author: rahulthebuilder

README.md

@@ -100,7 +100,7 @@ we move them into the [Alumni section](#alumni-) below.
 | [SelectiveClipboardFormatRead](ClipboardAPI/SelectiveClipboardFormatRead/explainer.md) | <a href="https://github.com/MicrosoftEdge/MSEdgeExplainers/labels/SelectiveClipboardFormatRead">![GitHub issues by-label](https://img.shields.io/github/issues/MicrosoftEdge/MSEdgeExplainers/SelectiveClipboardFormatRead?label=issues)</a> | [New Issue...](https://github.com/MicrosoftEdge/MSEdgeExplainers/issues/new?template=selective-clipboard-format-read.md) | Editing |
 | [Page Interaction Restriction Manager](PageInteractionRestrictionManager/explainer.md) | <a href="https://github.com/MicrosoftEdge/MSEdgeExplainers/labels/Page%20Interaction%20Restriction%20Manager">![GitHub issues by-label](https://img.shields.io/github/issues/MicrosoftEdge/MSEdgeExplainers/Page%20Interaction%20Restriction%20Manager?label=issues)</a> | [New issue...](https://github.com/MicrosoftEdge/MSEdgeExplainers/issues/new?template=page-interaction-restriction-manager.md) | Enterprise |
 | [DataTransferForInputEvent](Editing/input-event-dataTransfer-explainer.md) | <a href="https://github.com/MicrosoftEdge/MSEdgeExplainers/labels/DataTransferForInputEvent">![GitHub issues by-label](https://img.shields.io/github/issues/MicrosoftEdge/MSEdgeExplainers/DataTransferForInputEvent?label=issues)</a> | [New Issue...](https://github.com/MicrosoftEdge/MSEdgeExplainers/issues/new?template=data-transfer-for-input-event.md) | Editing |
-| [RTCRtpReceiver Decoder Fallback](RTCRtpReceiverDecoderFallback/explainer.md) | <a href="https://github.com/MicrosoftEdge/MSEdgeExplainers/labels/RTCRtpReceiverDecoderFallback">![GitHub issues by-label](https://img.shields.io/github/issues/MicrosoftEdge/MSEdgeExplainers/RTCRtpReceiverDecoderFallback?label=issues)</a> | [New Issue...](https://github.com/MicrosoftEdge/MSEdgeExplainers/issues/new?assignees=nishitha-burman&labels=RTCRtpReceiverDecoderFallback&title=%5BRTCRtpReceiver+Decoder+Fallback%5D+%3CTITLE+HERE%3E) | WebRTC |
+| [RTCRtpReceiver Decoder State Changed and Error Events](RTCRtpReceiverDecoderFallback/explainer.md) | <a href="https://github.com/MicrosoftEdge/MSEdgeExplainers/labels/RTCRtpReceiverDecoderFallback">![GitHub issues by-label](https://img.shields.io/github/issues/MicrosoftEdge/MSEdgeExplainers/RTCRtpReceiverDecoderFallback?label=issues)</a> | [New Issue...](https://github.com/MicrosoftEdge/MSEdgeExplainers/issues/new?assignees=nishitha-burman&labels=RTCRtpReceiverDecoderFallback&title=%5BRTCRtpReceiver+Decoder+State+Changed+and+Error+Events%5D+%3CTITLE+HERE%3E) | WebRTC |
 | [Offline Audio Context Streaming](OfflineAudioContext/explainer.md) | <a href="https://github.com/MicrosoftEdge/MSEdgeExplainers/labels/OfflineAudioContextStreaming">![GitHub issues by-label](https://img.shields.io/github/issues/MicrosoftEdge/MSEdgeExplainers/OfflineAudioContextStreaming?label=issues)</a> | [New Issue...](https://github.com/MicrosoftEdge/MSEdgeExplainers/issues/new?assignees=nishitha-burman&labels=OfflineAudioContextStreaming&title=%5BOfflineAudioContextStreaming%5D+%3CTITLE+HERE%3E) | Audio |
 | [Network Efficiency Guardrails](PerformanceControlOfEmbeddedContent/neg-explainer.md) | <a href="https://github.com/MicrosoftEdge/MSEdgeExplainers/labels/Network%20Efficiency%20Guardrails">![GitHub issues by-label](https://img.shields.io/github/issues/MicrosoftEdge/MSEdgeExplainers/Network%20Efficiency%20Guardrails?label=issues)</a> | [New Issue...](https://github.com/MicrosoftEdge/MSEdgeExplainers/issues/new?template=network-efficiency-guardrails.md) | WICG |
 | [Conditional Tracing for LoAF](ConditionalTracing/explainer-for-loaf.md) | <a href="https://github.com/MicrosoftEdge/MSEdgeExplainers/labels/Conditional%20Tracing%20for%20LoAF">![GitHub issues by-label](https://img.shields.io/github/issues/MicrosoftEdge/MSEdgeExplainers/Conditional%20Tracing%20for%20LoAF?label=issues)</a> | [New Issue...](https://github.com/MicrosoftEdge/MSEdgeExplainers/issues/new?template=conditonal-tracing-loaf.md) | Web Perf |