Modify the AConfig flag name for Glasses

It doesn't allow to have two same declaration in the same package.

Bug: 432240117
Bug: 430302860
Flag: com.android.microxr.xr_glasses_feature
Test: m com.android.microxr.flags-aconfig-java, m update-api
Change-Id: I9f83562bee0fba2b99209e68ae0c654b2b1dbb77