Support text highlighting in st.pdf

[asaini]

Checklist

• I have searched the existing issues for similar feature requests.
• I added a descriptive title and summary to this issue.

Summary

Users want to be able to highlight text in st.pdf

This helps in making references in the PDF doc clear, or be able to perform some action in the regular app and have it get highlighted in the PDF document

Why?

No response

How?

No response

Additional Context

No response

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