Fix subtle copying bug in primeShaderCache

Move the declaration of vectors to the innermost loop that uses them.

We loop through a bunch of different LayerSettings to draw content that
will prime the shader cache. In several places, we create a vector
initialized with multiple LayerSettings, and then inside a loop, we
modify the originals. When this code was written, we created a
vector<const LayerSettings*>. In
I87847d01e2e330ddec88272cd8608f0b78c0a2cd, the RenderEngine API was
changed to accept a vector<LayerSettings>. The problem is, when
constructing a vector<LayerSettings>, we get a *copy* of the items in
the initializer list. So when the loop modifies the originals, the
vector stays as it is, and only the first iteraton of the loop caches
any shaders. On my test device, we have only cached 6 shaders at the end
of primeShaderCache. With this change, we are back up to 93 shaders.

Bug: 190487656
Bug: 222355787
Test: manual - logcat + perfetto
Change-Id: I9f0e9e8535feee48700f1c896f26833b6095764d