Add polyphonic character modifications

[tengsimin]

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1. Is this request related to a challenge you're experiencing? Tell me about your story.

After listening to some synthesized effects, the accuracy on Chinese polyphonic characters is still not high. Can ssml be supported to modify pronunciation, such as in the following case

eg：

1. 单老师说，单于只会骑马，不会骑单车
2. 尽管他生活一直没宁静过，但他宁死不屈，也不息事宁人

2. Additional context or comments

No response

3. Can you help us with this feature?

• [ ] I am interested in contributing to this feature.