Implement PR feedback for Extended HE-AAC

- Adds "(xHE-AAC)" to the display name of mp4a.40.42
- Changes "shall" to "must" in EncodedAudioChunk data requirement

Co-authored-by: Djuffin <132926+Djuffin@users.noreply.github.com>

Author: google-labs-jules[bot]

aac_codec_registration.src.html

@@ -66,7 +66,7 @@
 - `"mp4a.40.5"` — MPEG-4 HE-AAC v1 (AAC LC + SBR)
 - `"mp4a.40.05"` — MPEG-4 HE-AAC v1 (AAC LC + SBR), leading 0 for Aud-OTI compatibility
 - `"mp4a.40.29"` — MPEG-4 HE-AAC v2 (AAC LC + SBR + PS)
-- `"mp4a.40.42"` — Extended HE-AAC (MPEG-D USAC + MPEG-D DRC) as defined in [[iso23003-3]] and [[iso23003-4]]
+- `"mp4a.40.42"` — Extended HE-AAC (xHE-AAC) (MPEG-D USAC + MPEG-D DRC) as defined in [[iso23003-3]] and [[iso23003-4]]
 - `"mp4a.67"` — MPEG-2 AAC LC
 
 EncodedAudioChunk data {#encodedaudiochunk-data}
@@ -79,7 +79,7 @@
 If the bitstream is in {{AacBitstreamFormat/aac}} format, the
 {{EncodedAudioChunk/[[internal data]]}} of {{EncodedAudioChunk}}s are expected
 to be a raw AAC frame (syntax element `raw_data_block()`), as described in
-section 4.4.2.1 of [[iso14496-3]]. Extended HE-AAC shall be in {{AacBitstreamFormat/aac}} format.
+section 4.4.2.1 of [[iso14496-3]]. Extended HE-AAC must be in {{AacBitstreamFormat/aac}} format.
 
 AudioDecoderConfig description {#audiodecoderconfig-description}
 ================================================================