Converts lingering panic alert calls over to the fmt-capable ones.

Migrates the logging over to the fmt-capable logger.

Now that we've extracted all of the stateless functions that can be
hidden, it's time to make the index generator a regular class with
active data members.

This can just be a member that sits within the vertex manager base
class. By deglobalizing the state of the index generator we also get rid
of the wonky dual-initializing that was going on within the OpenGL
backend.

Since the renderer is always initialized before the vertex manager, we
now only call Init() once throughout the execution lifecycle.

Makes the global variable follow our convention of prefixing g_ on
global variables to make it obvious in surrounding code that it's not a
local variable.

Normalizes all variables related to statistics so that they follow our
coding style.

These are relatively low traffic areas, so this modification isn't too
noisy.