Use a Unicode-compatible default font (for subscripts and symbols)

[kyleelowande-a11y]

Hi ReportLab team,

I wanted to share a quick suggestion that could really improve usability for many users — especially in science, education, and international contexts.

Currently, the default ReportLab font (Helvetica) doesn’t support Unicode subscripts, superscripts, or many special characters. This often causes black squares (“�”) to appear when creating documents that include chemical formulas (like H₃PO₄ or CO₂), mathematical notation, or non-Latin text.

Switching the default to a Unicode-compatible font such as DejaVu Sans or Arial Unicode MS would solve this issue and ensure correct rendering for all common scientific and multilingual text. Even if Helvetica remained the default, adding a clear note or fallback mechanism in the documentation would help users avoid confusion.

Thank you for maintaining such a powerful library — it’s an incredible tool for generating professional PDFs in Python!