opengl: tests: Add explict android:exported flag to manifests

After Android S+, it's required to add android:exported flag on manifests
if an intent filter is defined[1]. However, it's missing on the
manifests of these opengl tests which are targeting to current sdk
version leads to installation failures for these APKs. Fix it by adding
required android:exported flag.

[1]: https://android.googlesource.com/platform/frameworks/base/+/c4e90ac06ad3e0fd2af9e3864742e2d1199a8cdd

Test: These APKs are installed successfully on Android 12 devices.

Bug: 215940253
Change-Id: Ia95a46cc55103e7f075900acd237b41699f4cbd0