feat: [TextToSpeech] Support HD voice custom pronunciations (#8198)

* feat: Support HD voice custom pronunciations
docs: A comment for method `StreamingSynthesize` in service `TextToSpeech` is changed
docs: A comment for enum value `OGG_OPUS` in enum `AudioEncoding` is changed
docs: A comment for enum value `PCM` in enum `AudioEncoding` is changed
docs: A comment for field `low_latency_journey_synthesis` in message `.google.cloud.texttospeech.v1.AdvancedVoiceOptions` is changed
docs: A comment for enum value `PHONETIC_ENCODING_IPA` in enum `PhoneticEncoding` is changed
docs: A comment for enum value `PHONETIC_ENCODING_X_SAMPA` in enum `PhoneticEncoding` is changed
docs: A comment for field `phrase` in message `.google.cloud.texttospeech.v1.CustomPronunciationParams` is changed
docs: A comment for field `pronunciations` in message `.google.cloud.texttospeech.v1.CustomPronunciations` is changed
docs: A comment for message `MultiSpeakerMarkup` is changed
docs: A comment for field `custom_pronunciations` in message `.google.cloud.texttospeech.v1.SynthesisInput` is changed
docs: A comment for field `voice_clone` in message `.google.cloud.texttospeech.v1.VoiceSelectionParams` is changed
docs: A comment for field `audio_encoding` in message `.google.cloud.texttospeech.v1.StreamingAudioConfig` is changed
docs: A comment for field `text` in message `.google.cloud.texttospeech.v1.StreamingSynthesisInput` is changed

PiperOrigin-RevId: 742280480

Source-Link: googleapis/googleapis@2059f0f

Source-Link: googleapis/googleapis-gen@1308d49
Copy-Tag: eyJwIjoiVGV4dFRvU3BlZWNoLy5Pd2xCb3QueWFtbCIsImgiOiIxMzA4ZDQ5NTIxY2Q4YWZlODZmMjFlMmI1YzFjNDM3Mzg3MWUxMzVkIn0=

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gcf-owl-bot[bot]

TextToSpeech/metadata/V1/CloudTts.php

@@ -30,7 +30,7 @@
 use Google\Cloud\TextToSpeech\V1\StreamingSynthesizeResponse;
 
 /**
- * Performs bidirectional streaming speech synthesis: receive audio while
+ * Performs bidirectional streaming speech synthesis: receives audio while
  * sending text.
  *
  * This sample has been automatically generated and should be regarded as a code

TextToSpeech/samples/V1/TextToSpeechClient/streaming_synthesize.php

@@ -250,7 +250,7 @@ public function listVoices(ListVoicesRequest $request, array $callOptions = []):
     }
 
     /**
-     * Performs bidirectional streaming speech synthesis: receive audio while
+     * Performs bidirectional streaming speech synthesis: receives audio while
      * sending text.
      *
      * @example samples/V1/TextToSpeechClient/streaming_synthesize.php