graphics/hugin: permit use of libepoxy instead of glew

Some users report problems with hugin coming from graphics/glew not
being built with EGL support. Permit using libepoxy instead of
graphics/glew for OpenGL stuff and make it the default to work around
this issue. Building with graphics/glew remains available as an option.

PR: 296330, 296368
Reported by: grog
Tested by: grog
MFH: 2026Q2

(cherry picked from commit 2fa6358ccc39f9ef705ca209fc9dacf276ef69df)