Rename Glyphs custom parameter handler doesn't affect kerning

I don't need this in glyphsLib but I discovered in when working on babelfont: The Glyphs "Rename Glyphs" custom parameter also swaps the names of glyphs in the kerning tables as well; we just swap the outlines, meaning the kerning (or lack of kerning) of the old glyph is applied to the new glyph.

Start by tracing how the Glyphs "Rename Glyphs" custom parameter is handled and where kerning tables are converted. Verify how glyph-name swaps affect outlines versus kerning, then confirm the fix by checking that kerning follows the renamed glyphs, including cases with no kerning.

Written by the indexing model from the issue text.