graphics/inkscape: update to 1.2.1 release (+)

This update provides a fix for a number of critical bugs in the 1.2 release:

• drawing data about filters, markers, gradients and more now saves to file after performing a simple sequence of copy-paste-undo with the Export dialog open;
• startup is smoother when many fonts are installed, and
• rasterized (filtered) objects now show up on any page of a multipage document exported to PDF.

While here, point Makefile to use C++17 standard as it assumed upstream

Release notes: https://media.inkscape.org/media/doc/release_notes/1.2.1/Inkscape_1.2.1.html