DOC: Add a release note for PDF font embedding fixes

Author: QuLogic

doc/release/next_whats_new/pdf_fonts.rst

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+Improved font embedding in PDF
+------------------------------
+
+Both Type 3 and Type 42 fonts (see :ref:`fonts` for more details) are now
+embedded into PDFs without limitation. Fonts may be split into multiple
+embedded subsets in order to satisfy format limits. Additionally, a corrected
+Unicode mapping is added for each.
+
+This means that *all* text should now be selectable and copyable in PDF viewers
+that support doing so.