handle end-of-line selection correctly. Stop highlighting selection on

* src/vte.c: handle end-of-line selection correctly.  Stop highlighting
	selection on click, but don't lose it until new text is selected.
* python/vte.override: fix binding for set_colors() to properly take a
	list of colors for the palette (#97682).
* src/vte.c, src/vte.h: add increase-font-size and decrease-font-size to allow
	mimicking XTerm's and Mozilla's behavior on Shift/Control
	KP_Add/KP_Subtract
* src/vteapp.c: handle increase-font-size and decrease-font-size.