RootlessGpuDebug: Change Activity to Service

On platforms that use Vulkan exclusively, we're tripping up Activity
start when we launch negative tests (i.e. those that expect to FAIL
when launching with layers that cannot be accessed).  We don't even
make it to our test code before our process has been terminated due
to failed vkCreateInstance calls in platform code.

In order to avoid complications with how the platform renders the
empty Activity, this CL switches to a background Service that doesn't
render anything.

This test really only wants to init Vulkan and GLES itself in native
code, then observe loader and layer behavior.

Test: CtsGpuToolsHostTestCases on Cuttlefish using SkiaVk
Bug: b/206011745
Bug: b/206023179
Change-Id: Icbeab9850e24ead6ffd996a5531f32cd5da37035
(cherry picked from commit f7411f644badc1a582249aa98db062dfc769d873)
6 files changed