Check GL extension is supported before using it in glwallpaper

glwallpaper requests a GL context with low priority, however this
feature is a GL extension that may not be available in the GL
implementation (swiftshader, for example).

Bug: 138834844
Test: run cuttlefish locally
Merged-In: I72edeb0f4dc03e51bda22209415604e752c18e52
Change-Id: I72edeb0f4dc03e51bda22209415604e752c18e52