Library gaps songformatter hit: Menu.tk_popup, Menu.entryconfigure, pdfmetrics.getRegisteredFontNames

From the songformatter session's build report (2026-10-27); the patch was written there and applied as is:

• lib/pcl/mimic_reportlab_pdfbase_pdfmetrics.pas forwarded only stringWidth, so pdfmetrics.getRegisteredFontNames() was "no member". It now forwards it (the function already existed in mimic_reportlab_pdfbase).
• tkinter Menu.tk_popup(x, y): Tk's own popup helper.
• tkinter Menu.entryconfigure(index, label=, state=): the index may be an entry LABEL, which is how the app calls it (menu.entryconfigure("Save", state=...)).
• Widget.withdraw() and Widget.state() (wm withdraw / wm state), for the hidden-root idiom tk.Tk().withdraw(). Checked against CPython under Xvfb.